diff --git a/C/absmi.c b/C/absmi.c
index bf2c4780d..9bec5a3c3 100644
--- a/C/absmi.c
+++ b/C/absmi.c
@@ -2532,7 +2532,7 @@ Yap_absmi(int inp)
 	ENDP(pt1);
       }
       ENDD(d0);
-      H[0] = Yap_Module_Name(((CODEADDR)(SREG)));
+      H[0] = Yap_Module_Name((PredEntry *)SREG);
       ARG1 = (Term) AbsPair(H);
 
       H += 2;
@@ -6434,7 +6434,7 @@ Yap_absmi(int inp)
 	  ENDP(pt1);
 	}
 	ENDD(d0);
-	H[0] = Yap_Module_Name((CODEADDR)pe);
+	H[0] = Yap_Module_Name(pe);
 	ARG1 = (Term) AbsPair(H);
 	H += 2;
       }
@@ -6498,7 +6498,7 @@ Yap_absmi(int inp)
 	  ENDP(pt1);
 	}
 	ENDD(d0);
-	H[0] = Yap_Module_Name((CODEADDR)pe);
+	H[0] = Yap_Module_Name(pe);
       }
       ARG1 = (Term) AbsPair(H);
       H += 2;
@@ -11279,7 +11279,7 @@ Yap_absmi(int inp)
       BOp(p_execute, sla);
       { 
 	PredEntry *pen;
-	SMALLUNSGN mod = PREG->u.sla.sla_u.m_num;
+	Term mod = PREG->u.sla.sla_u.mod;
 
 	CACHE_Y_AS_ENV(YREG);
 	/* Try to preserve the environment */
@@ -11314,7 +11314,7 @@ Yap_absmi(int inp)
 	      Term tmod = ArgOfTerm(1,d0);
 	      if (!IsVarTerm(tmod) && IsAtomTerm(tmod)) {
 		d0 = ArgOfTerm(2,d0);
-		mod = Yap_LookupModule(tmod);
+		mod = tmod;
 		goto execute_nvar;
 	      }
 	    } else if (f == FunctorComma) {
@@ -11431,7 +11431,10 @@ Yap_absmi(int inp)
 	ARG1 = ARG3 = d0;
 	pen = PredMetaCall;
 	ARG2 = Yap_cp_as_integer(B);
-	ARG4 = ModuleName[mod];
+	if (mod)
+	  ARG4 = mod;
+	else
+	  ARG4 = TermProlog;
 	CACHE_A1();
 	goto execute_end;
 	ENDP(pt1);
@@ -11462,7 +11465,7 @@ Yap_absmi(int inp)
       BOp(p_execute_tail, e);
       {
 	PredEntry *pen;
-	SMALLUNSGN mod;
+	Term mod;
 	UInt arity;
 
 	CACHE_Y_AS_ENV(YREG);
@@ -11513,7 +11516,7 @@ Yap_absmi(int inp)
 		Term tmod = ArgOfTerm(1, d1);
 		if (IsVarTerm(tmod) || !IsAtomTerm(tmod))
 		  goto execute_metacall_after_comma;
-		mod = Yap_LookupModule(tmod);
+		mod = tmod;
 		d1 = RepAppl(d1)[2];
 		goto execute_comma_comma;
 	      } else {
@@ -11565,7 +11568,7 @@ Yap_absmi(int inp)
 		Term tmod = ArgOfTerm(1, d0);
 		if (IsVarTerm(tmod) || !IsAtomTerm(tmod))
 		  goto execute_metacall_after_comma;
-		mod = Yap_LookupModule(tmod);
+		mod = tmod;
 		d0 = RepAppl(d0)[2];
 		goto execute_comma_comma2;
 	      } else {
@@ -11601,7 +11604,10 @@ Yap_absmi(int inp)
 	      ARG1 = ARG3 = d0;
 	      pen = PredMetaCall;
 	      ARG2 = Yap_cp_as_integer((choiceptr)pt0[E_CB]);
-	      ARG4 = ModuleName[mod];
+	      if (mod)
+		ARG4 = mod;
+	      else
+		ARG4 = TermProlog;
 	      CACHE_A1();
 	      goto execute_after_comma;
 	    }
diff --git a/C/adtdefs.c b/C/adtdefs.c
index 45ca800bf..5869f063b 100644
--- a/C/adtdefs.c
+++ b/C/adtdefs.c
@@ -27,8 +27,8 @@ static char SccsId[] = "%W% %G%";
 
 #include "Yap.h"
 ADDR    STD_PROTO(Yap_PreAllocCodeSpace, (void));
-Prop	STD_PROTO(PredPropByFunc,(Functor, SMALLUNSGN));
-Prop	STD_PROTO(PredPropByAtom,(Atom, SMALLUNSGN));
+Prop	STD_PROTO(PredPropByFunc,(Functor, Term));
+Prop	STD_PROTO(PredPropByAtom,(Atom, Term));
 #include "Yatom.h"
 #include "Heap.h"
 #include "yapio.h"
@@ -300,7 +300,7 @@ Yap_GetAProp(Atom a, PropFlags kind)
 }
 
 inline static Prop
-GetPredPropByAtomHavingLock(AtomEntry* ae, SMALLUNSGN cur_mod)
+GetPredPropByAtomHavingLock(AtomEntry* ae, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
@@ -324,7 +324,7 @@ GetPredPropByAtomHavingLock(AtomEntry* ae, SMALLUNSGN cur_mod)
 }
 
 Prop
-Yap_GetPredPropByAtom(Atom at, SMALLUNSGN cur_mod)
+Yap_GetPredPropByAtom(Atom at, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
@@ -338,7 +338,7 @@ Yap_GetPredPropByAtom(Atom at, SMALLUNSGN cur_mod)
 
 
 inline static Prop
-GetPredPropByAtomHavingLockInThisModule(AtomEntry* ae, SMALLUNSGN cur_mod)
+GetPredPropByAtomHavingLockInThisModule(AtomEntry* ae, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
@@ -361,7 +361,7 @@ GetPredPropByAtomHavingLockInThisModule(AtomEntry* ae, SMALLUNSGN cur_mod)
 }
 
 Prop
-Yap_GetPredPropByAtomInThisModule(Atom at, SMALLUNSGN cur_mod)
+Yap_GetPredPropByAtomInThisModule(Atom at, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
@@ -375,7 +375,7 @@ Yap_GetPredPropByAtomInThisModule(Atom at, SMALLUNSGN cur_mod)
 
 
 static inline Prop
-GetPredPropByFuncHavingLock(Functor f, SMALLUNSGN cur_mod)
+GetPredPropByFuncHavingLock(Functor f, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
@@ -400,7 +400,7 @@ GetPredPropByFuncHavingLock(Functor f, SMALLUNSGN cur_mod)
 }
 
 Prop
-Yap_GetPredPropByFunc(Functor f, SMALLUNSGN cur_mod)
+Yap_GetPredPropByFunc(Functor f, Term cur_mod)
      /* get predicate entry for ap/arity;               */
 {
   Prop p0;
@@ -412,7 +412,7 @@ Yap_GetPredPropByFunc(Functor f, SMALLUNSGN cur_mod)
 }
 
 static inline Prop
-GetPredPropByFuncHavingLockInThisModule(Functor f, SMALLUNSGN cur_mod)
+GetPredPropByFuncHavingLockInThisModule(Functor f, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
@@ -436,7 +436,7 @@ GetPredPropByFuncHavingLockInThisModule(Functor f, SMALLUNSGN cur_mod)
 }
 
 Prop
-Yap_GetPredPropByFuncInThisModule(Functor f, SMALLUNSGN cur_mod)
+Yap_GetPredPropByFuncInThisModule(Functor f, Term cur_mod)
      /* get predicate entry for ap/arity;               */
 {
   Prop p0;
@@ -448,7 +448,7 @@ Yap_GetPredPropByFuncInThisModule(Functor f, SMALLUNSGN cur_mod)
 }
 
 Prop
-Yap_GetPredPropHavingLock(Atom ap, unsigned int arity, SMALLUNSGN mod)
+Yap_GetPredPropHavingLock(Atom ap, unsigned int arity, Term mod)
      /* get predicate entry for ap/arity;               */
 {
   Prop p0;
@@ -496,7 +496,7 @@ Yap_GetExpPropHavingLock(AtomEntry *ae, unsigned int arity)
 
 /* fe is supposed to be locked */
 Prop
-Yap_NewPredPropByFunctor(FunctorEntry *fe, SMALLUNSGN cur_mod)
+Yap_NewPredPropByFunctor(FunctorEntry *fe, Term cur_mod)
 {
   Prop p0;
   PredEntry *p = (PredEntry *) Yap_AllocAtomSpace(sizeof(*p));
@@ -512,9 +512,11 @@ Yap_NewPredPropByFunctor(FunctorEntry *fe, SMALLUNSGN cur_mod)
   p->OpcodeOfPred = UNDEF_OPCODE;
   p->CodeOfPred = p->cs.p_code.TrueCodeOfPred = (yamop *)(&(p->OpcodeOfPred)); 
   p->cs.p_code.ExpandCode = EXPAND_OP_CODE; 
-  p->ModuleOfPred = cur_mod;
-  p->NextPredOfModule = ModulePred[cur_mod];
-  ModulePred[cur_mod] = p;
+  if (cur_mod == TermProlog)
+    p->ModuleOfPred = 0;
+  else
+    p->ModuleOfPred = cur_mod;
+  Yap_NewModulePred(cur_mod, p);
   INIT_LOCK(p->StatisticsForPred.lock);
   p->StatisticsForPred.NOfEntries = 0;
   p->StatisticsForPred.NOfHeadSuccesses = 0;
@@ -565,12 +567,12 @@ Yap_NewThreadPred(PredEntry *ap)
 #endif
 
 Prop
-Yap_NewPredPropByAtom(AtomEntry *ae, SMALLUNSGN cur_mod)
+Yap_NewPredPropByAtom(AtomEntry *ae, Term cur_mod)
 {
   Prop p0;
   PredEntry *p = (PredEntry *) Yap_AllocAtomSpace(sizeof(*p));
 
-/* Printf("entering %s:%s/0\n", RepAtom(AtomOfTerm(ModuleName[cur_mod]))->StrOfAE, ae->StrOfAE); */
+/* Printf("entering %s:%s/0\n", RepAtom(AtomOfTerm(cur_mod))->StrOfAE, ae->StrOfAE); */
 
   INIT_RWLOCK(p->PRWLock);
   INIT_LOCK(p->PELock);
@@ -583,9 +585,11 @@ Yap_NewPredPropByAtom(AtomEntry *ae, SMALLUNSGN cur_mod)
   p->OpcodeOfPred = UNDEF_OPCODE;
   p->cs.p_code.ExpandCode = EXPAND_OP_CODE; 
   p->CodeOfPred = p->cs.p_code.TrueCodeOfPred = (yamop *)(&(p->OpcodeOfPred)); 
-  p->ModuleOfPred = cur_mod;
-  p->NextPredOfModule = ModulePred[cur_mod];
-  ModulePred[cur_mod] = p;
+  if (cur_mod == TermProlog)
+    p->ModuleOfPred = 0;
+  else
+    p->ModuleOfPred = cur_mod;
+  Yap_NewModulePred(cur_mod, p);
   INIT_LOCK(p->StatisticsForPred.lock);
   p->StatisticsForPred.NOfEntries = 0;
   p->StatisticsForPred.NOfHeadSuccesses = 0;
@@ -602,7 +606,7 @@ Yap_NewPredPropByAtom(AtomEntry *ae, SMALLUNSGN cur_mod)
 }
 
 Prop
-Yap_PredPropByFunctorNonThreadLocal(Functor f, SMALLUNSGN cur_mod)
+Yap_PredPropByFunctorNonThreadLocal(Functor f, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
@@ -623,7 +627,7 @@ Yap_PredPropByFunctorNonThreadLocal(Functor f, SMALLUNSGN cur_mod)
 }
 
 Prop
-Yap_PredPropByAtomNonThreadLocal(Atom at, SMALLUNSGN cur_mod)
+Yap_PredPropByAtomNonThreadLocal(Atom at, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
diff --git a/C/amasm.c b/C/amasm.c
index b9a5cf8a8..cf05a7a9a 100644
--- a/C/amasm.c
+++ b/C/amasm.c
@@ -822,7 +822,7 @@ a_p(op_numbers opcode, clause_info *clinfo, yamop *code_p, int pass_no, struct i
 	if (RepPredProp(fe)->FunctorOfPred != FunctorExecuteInMod) {
 	  code_p->u.sla.sla_u.p =  RepPredProp(fe);
 	} else {
-	  code_p->u.sla.sla_u.m_num =  IntegerOfTerm(cip->cpc->rnd4);
+	  code_p->u.sla.sla_u.mod =  cip->cpc->rnd4;
 	}
 	code_p->u.sla.p0 =  clinfo->CurrentPred;
 	if (cip->cpc->rnd2) {
diff --git a/C/bb.c b/C/bb.c
index 808fc306c..cee283cef 100644
--- a/C/bb.c
+++ b/C/bb.c
@@ -26,7 +26,7 @@ static char     SccsId[] = "%W% %G%";
 #endif
 
 static BBProp 
-PutBBProp(AtomEntry *ae, SMALLUNSGN mod)		/* get BBentry for at; */
+PutBBProp(AtomEntry *ae, Term mod)		/* get BBentry for at; */
 {
   Prop          p0;
   BBProp        p;
@@ -57,7 +57,7 @@ PutBBProp(AtomEntry *ae, SMALLUNSGN mod)		/* get BBentry for at; */
 }
 
 static BBProp 
-PutIntBBProp(Int key, SMALLUNSGN mod)	/* get BBentry for at; */
+PutIntBBProp(Int key, Term mod)	/* get BBentry for at; */
 {
   Prop          p0;
   BBProp        p;
@@ -105,7 +105,7 @@ PutIntBBProp(Int key, SMALLUNSGN mod)	/* get BBentry for at; */
 }
 
 static BBProp 
-GetBBProp(AtomEntry *ae, SMALLUNSGN mod)		/* get BBentry for at; */
+GetBBProp(AtomEntry *ae, Term mod)		/* get BBentry for at; */
 {
   Prop          p0;
   BBProp        p;
@@ -124,7 +124,7 @@ GetBBProp(AtomEntry *ae, SMALLUNSGN mod)		/* get BBentry for at; */
 }
 
 static BBProp 
-GetIntBBProp(Int key, SMALLUNSGN mod)		/* get BBentry for at; */
+GetIntBBProp(Int key, Term mod)		/* get BBentry for at; */
 {
   Prop          p0;
   BBProp        p;
@@ -187,7 +187,7 @@ resize_bb_int_keys(UInt new_size) {
 }
 
 static BBProp
-AddBBProp(Term t1, char *msg, SMALLUNSGN mod)
+AddBBProp(Term t1, char *msg, Term mod)
 {
   BBProp p;
 
@@ -203,7 +203,7 @@ AddBBProp(Term t1, char *msg, SMALLUNSGN mod)
     Term tmod = ArgOfTerm(1, t1);
     if (!IsVarTerm(tmod) ) {
       t1 = ArgOfTerm(2, t1);
-      mod = Yap_LookupModule(tmod);
+      mod = tmod;
       goto restart;
     } else {
       Yap_Error(INSTANTIATION_ERROR, t1, msg);
@@ -217,7 +217,7 @@ AddBBProp(Term t1, char *msg, SMALLUNSGN mod)
 }
 
 static BBProp
-FetchBBProp(Term t1, char *msg, SMALLUNSGN mod)
+FetchBBProp(Term t1, char *msg, Term mod)
 {
   BBProp p;
 
@@ -232,7 +232,7 @@ FetchBBProp(Term t1, char *msg, SMALLUNSGN mod)
   } else if (IsApplTerm(t1) && FunctorOfTerm(t1) == FunctorModule) {
     Term tmod = ArgOfTerm(1, t1);
     if (!IsVarTerm(tmod) ) {
-      mod = Yap_LookupModule(tmod);
+      mod = tmod;
       t1 = ArgOfTerm(2, t1);
       goto restart;
     } else {
diff --git a/C/c_interface.c b/C/c_interface.c
index 74c5f898e..417596b7b 100644
--- a/C/c_interface.c
+++ b/C/c_interface.c
@@ -114,7 +114,6 @@ X_API Term   *STD_PROTO(YAP_AddressFromSlot,(long));
 X_API void    STD_PROTO(YAP_PutInSlot,(long, Term));
 X_API void    STD_PROTO(YAP_RecoverSlots,(int));
 X_API void    STD_PROTO(YAP_Throw,(Term));
-X_API int     STD_PROTO(YAP_LookupModule,(Term));
 X_API Term    STD_PROTO(YAP_ModuleName,(int));
 X_API void    STD_PROTO(YAP_Halt,(int));
 X_API Term   *STD_PROTO(YAP_TopOfLocalStack,(void));
@@ -122,7 +121,7 @@ X_API void   *STD_PROTO(YAP_Predicate,(Atom,unsigned long int,int));
 X_API void    STD_PROTO(YAP_PredicateInfo,(void *,Atom *,unsigned long int *,int *));
 X_API void    STD_PROTO(YAP_UserCPredicate,(char *,CPredicate,unsigned long int));
 X_API void    STD_PROTO(YAP_UserBackCPredicate,(char *,CPredicate,CPredicate,unsigned long int,unsigned int));
-X_API void    STD_PROTO(YAP_UserCPredicateWithArgs,(char *,CPredicate,unsigned long int,int));
+X_API void    STD_PROTO(YAP_UserCPredicateWithArgs,(char *,CPredicate,unsigned long int,Term));
 X_API Int     STD_PROTO(YAP_CurrentModule,(void));
 
 static int (*do_getf)(void);
@@ -567,7 +566,7 @@ X_API Int
 YAP_CallProlog(Term t)
 {
   Int out;
-  SMALLUNSGN mod = CurrentModule;
+  Term mod = CurrentModule;
   BACKUP_MACHINE_REGS();
 
   while (!IsVarTerm(t) &&
@@ -576,7 +575,7 @@ YAP_CallProlog(Term t)
     Term tmod = ArgOfTerm(1,t);
     if (IsVarTerm(tmod)) return(FALSE);
     if (!IsAtomTerm(tmod)) return(FALSE);
-    mod = Yap_LookupModule(tmod);
+    mod = tmod;
     t = ArgOfTerm(2,t);
   }
   out = Yap_execute_goal(t, 0, mod);
@@ -1080,18 +1079,6 @@ YAP_Throw(Term t)
   RECOVER_MACHINE_REGS();
 }
 
-X_API int
-YAP_LookupModule(Term t)
-{
-  return(Yap_LookupModule(t));
-}
-
-X_API Term
-YAP_ModuleName(int i)
-{
-  return(ModuleName[i]);
-}
-
 X_API void
 YAP_Halt(int i)
 {
@@ -1126,7 +1113,10 @@ YAP_PredicateInfo(void *p, Atom* a, unsigned long int* arity, int* m)
     *arity = 0;
     *a = (Atom)(pd->FunctorOfPred);
   }
-  *m = pd->ModuleOfPred;
+  if (pd->ModuleOfPred)
+    *m = pd->ModuleOfPred;
+  else
+    *m = TermProlog;
 } 
 
 X_API void 
@@ -1143,10 +1133,10 @@ YAP_UserBackCPredicate(char *name, CPredicate init, CPredicate cont,
 }
 
 X_API void
-YAP_UserCPredicateWithArgs(char *a, CPredicate f, unsigned long int arity, int mod)
+YAP_UserCPredicateWithArgs(char *a, CPredicate f, unsigned long int arity, Term mod)
 {
   PredEntry *pe;
-  SMALLUNSGN cm = CurrentModule;
+  Term cm = CurrentModule;
   CurrentModule = mod;
   YAP_UserCPredicate(a,f,arity);
   if (arity == 0) {
diff --git a/C/cdmgr.c b/C/cdmgr.c
index f91bef1cc..4a1ecb994 100644
--- a/C/cdmgr.c
+++ b/C/cdmgr.c
@@ -79,7 +79,7 @@ STATIC_PROTO(Int  p_call_count_set, (void));
 STATIC_PROTO(Int  p_call_count_reset, (void));
 STATIC_PROTO(Int  p_toggle_static_predicates_in_use, (void));
 STATIC_PROTO(Atom  YapConsultingFile, (void));
-STATIC_PROTO(Int  PredForCode,(yamop *, Atom *, UInt *, SMALLUNSGN *));
+STATIC_PROTO(Int  PredForCode,(yamop *, Atom *, UInt *, Term *));
 
 #define PredArity(p) (p->ArityOfPE)
 #define TRYCODE(G,F,N) ( (N)<5 ? (op_numbers)((int)F+(N)*3) : G)
@@ -153,11 +153,13 @@ IPred(PredEntry *ap)
 
 #ifdef DEBUG
   if (Yap_Option['i' - 'a' + 1]) {
-    Term tmod = ModuleName[ap->ModuleOfPred];
+    Term tmod = ap->ModuleOfPred;
+    if (!tmod)
+      tmod = TermProlog;
     Yap_DebugPutc(Yap_c_error_stream,'\t');
     Yap_plwrite(tmod, Yap_DebugPutc, 0);
     Yap_DebugPutc(Yap_c_error_stream,':');
-    if (ap->ModuleOfPred == 2) {
+    if (ap->ModuleOfPred == IDB_MODULE) {
       Term t = Deref(ARG1);
       if (IsAtomTerm(t)) {
 	Yap_plwrite(t, Yap_DebugPutc, 0);
@@ -1058,7 +1060,8 @@ addclause(Term t, yamop *cp, int mode, int mod)
 #endif
   pflags = p->PredFlags;
   /* we are redefining a prolog module predicate */
-  if (p->ModuleOfPred == 0 && mod != 0) {
+  if (p->ModuleOfPred == PROLOG_MODULE && 
+      mod != TermProlog && mod) {
     WRITE_UNLOCK(p->PRWLock);
     addcl_permission_error(RepAtom(at), Arity, FALSE);
     return TermNil;
@@ -1143,12 +1146,12 @@ addclause(Term t, yamop *cp, int mode, int mod)
 }
 
 void
-Yap_addclause(Term t, yamop *cp, int mode, int mod) {
+Yap_addclause(Term t, yamop *cp, int mode, Term mod) {
   addclause(t, cp, mode, mod);
 }
 
 void
-Yap_EraseStaticClause(StaticClause *cl, SMALLUNSGN mod) {
+Yap_EraseStaticClause(StaticClause *cl, Term mod) {
   PredEntry *ap;
 
   /* ok, first I need to find out the parent predicate */
@@ -1264,7 +1267,7 @@ p_in_this_f_before(void)
   Term            t;
   register consult_obj  *fp;
   Prop            p0;
-  SMALLUNSGN      mod;
+  Term            mod;
 
   if (IsVarTerm(t = Deref(ARG1)) || !IsAtomTerm(t))
     return (FALSE);
@@ -1274,10 +1277,8 @@ p_in_this_f_before(void)
     return (FALSE);
   else
     arity = IntOfTerm(t);
-  if (IsVarTerm(t = Deref(ARG3)) || !IsAtomTerm(t))
-    return (FALSE);
-  else
-    mod = Yap_LookupModule(t);
+  if (IsVarTerm(mod = Deref(ARG3)) || !IsAtomTerm(mod))
+    return FALSE;
   if (arity)
     p0 = PredPropByFunc(Yap_MkFunctor(at, arity),CurrentModule);
   else
@@ -1303,7 +1304,7 @@ p_first_cl_in_f(void)
   Term            t;
   register consult_obj  *fp;
   Prop            p0;
-  SMALLUNSGN      mod;
+  Term	          mod;
   
 
   if (IsVarTerm(t = Deref(ARG1)) || !IsAtomTerm(t))
@@ -1314,10 +1315,8 @@ p_first_cl_in_f(void)
     return (FALSE);
   else
     arity = IntOfTerm(t);
-  if (IsVarTerm(t = Deref(ARG3)) || !IsAtomTerm(t))
+  if (IsVarTerm(mod = Deref(ARG3)) || !IsAtomTerm(mod))
     return (FALSE);
-  else
-    mod = Yap_LookupModule(t);
   if (arity)
     p0 = PredPropByFunc(Yap_MkFunctor(at, arity),mod);
   else
@@ -1379,16 +1378,14 @@ p_compile(void)
 {				/* '$compile'(+C,+Flags, Mod) */
   Term            t = Deref(ARG1);
   Term            t1 = Deref(ARG2);
-  Term            t3 = Deref(ARG4);
+  Term            mod = Deref(ARG4);
   yamop           *codeadr;
-  Int mod;
 
   if (IsVarTerm(t1) || !IsIntTerm(t1))
     return (FALSE);
-  if (IsVarTerm(t3) || !IsAtomTerm(t3))
+  if (IsVarTerm(mod) || !IsAtomTerm(mod))
     return (FALSE);
 
-  mod = Yap_LookupModule(t3);
   YAPEnterCriticalSection();
   codeadr = Yap_cclause(t, 2, mod, Deref(ARG3)); /* vsc: give the number of arguments
 			      to cclause in case there is overflow */
@@ -1412,18 +1409,16 @@ p_compile_dynamic(void)
 {				/* '$compile_dynamic'(+C,+Flags,Mod,-Ref) */
   Term            t = Deref(ARG1);
   Term            t1 = Deref(ARG2);
-  Term            t3 = Deref(ARG4);
+  Term            mod = Deref(ARG4);
   yamop        *code_adr;
   int             old_optimize;
-  Int mod;
 
   if (IsVarTerm(t1) || !IsIntTerm(t1))
     return (FALSE);
-  if (IsVarTerm(t3) || !IsAtomTerm(t3))
+  if (IsVarTerm(mod) || !IsAtomTerm(mod))
     return (FALSE);
   old_optimize = optimizer_on;
   optimizer_on = FALSE;
-  mod = Yap_LookupModule(t3);
   YAPEnterCriticalSection();
   code_adr = Yap_cclause(t, 3, mod, Deref(ARG3)); /* vsc: give the number of arguments to
 			       cclause() in case there is a overflow */
@@ -1595,16 +1590,14 @@ p_purge_clauses(void)
 {				/* '$purge_clauses'(+Func) */
   PredEntry      *pred;
   Term            t = Deref(ARG1);
-  Term            t2 = Deref(ARG2);
-  SMALLUNSGN      mod;
+  Term            mod = Deref(ARG2);
 
   Yap_PutValue(AtomAbol, MkAtomTerm(AtomNil));
   if (IsVarTerm(t))
-    return (FALSE);
-  if (IsVarTerm(t2) || !IsAtomTerm(t2)) {
-    return (FALSE);
+    return FALSE;
+  if (IsVarTerm(mod) || !IsAtomTerm(mod)) {
+    return FALSE;
   }
-  mod = Yap_LookupModule(t2);
   if (IsAtomTerm(t)) {
     Atom at = AtomOfTerm(t);
     pred = RepPredProp(PredPropByAtom(at, mod));
@@ -1645,20 +1638,17 @@ p_setspy(void)
   Atom            at;
   PredEntry      *pred;
   CELL            fg;
-  Term            t;
-  Term            t2;
-  SMALLUNSGN	  mod;
+  Term            t, mod;
 
   at = Yap_FullLookupAtom("$spy");
   pred = RepPredProp(PredPropByFunc(Yap_MkFunctor(at, 1),0));
   SpyCode = pred;
   t = Deref(ARG1);
-  t2 = Deref(ARG2);
+  mod = Deref(ARG2);
+  if (IsVarTerm(mod) || !IsAtomTerm(mod))
+    return (FALSE);
   if (IsVarTerm(t))
     return (FALSE);
-  if (IsVarTerm(t2) || !IsAtomTerm(t2))
-    return (FALSE);
-  mod = Yap_LookupModule(t2);
   if (IsAtomTerm(t)) {
     Atom at = AtomOfTerm(t);
     pred = RepPredProp(Yap_PredPropByAtomNonThreadLocal(at, mod));
@@ -1703,14 +1693,12 @@ p_rmspy(void)
   Atom            at;
   PredEntry      *pred;
   Term            t;
-  Term            t2;
-  SMALLUNSGN	  mod;
+  Term            mod;
 
   t = Deref(ARG1);
-  t2 = Deref(ARG2);
-  if (IsVarTerm(t2) || !IsAtomTerm(t2))
+  mod = Deref(ARG2);
+  if (IsVarTerm(mod) || !IsAtomTerm(mod))
     return (FALSE);
-  mod = Yap_LookupModule(t2);
   if (IsVarTerm(t))
     return (FALSE);
   if (IsAtomTerm(t)) {
@@ -1754,15 +1742,13 @@ static Int
 p_number_of_clauses(void)
 {				/* '$number_of_clauses'(Predicate,M,N) */
   Term            t = Deref(ARG1);
-  Term            t2 = Deref(ARG2);
+  Term            mod = Deref(ARG2);
   int ncl = 0;
   Prop            pe;
-  int             mod;
 
-  if (IsVarTerm(t2)  || !IsAtomTerm(t2)) {
+  if (IsVarTerm(mod)  || !IsAtomTerm(mod)) {
     return(FALSE);
   }
-  mod = Yap_LookupModule(t2);
   if (IsAtomTerm(t)) {
     Atom a = AtomOfTerm(t);
     pe = Yap_GetPredPropByAtom(a, mod);
@@ -1784,16 +1770,14 @@ static Int
 p_in_use(void)
 {				/* '$in_use'(+P,+Mod)	 */
   Term            t = Deref(ARG1);
-  Term            t2 = Deref(ARG2);
+  Term            mod = Deref(ARG2);
   PredEntry      *pe;
   Int            out;
-  int            mod;
 
   if (IsVarTerm(t))
     return (FALSE);
-  if (IsVarTerm(t2) || !IsAtomTerm(t2))
+  if (IsVarTerm(mod) || !IsAtomTerm(mod))
     return (FALSE);
-  mod = Yap_LookupModule(t2);
   if (IsAtomTerm(t)) {
     Atom at = AtomOfTerm(t);
     pe = RepPredProp(Yap_GetPredPropByAtom(at, mod));
@@ -1817,7 +1801,7 @@ p_new_multifile(void)
   int             arity;
   PredEntry      *pe;
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG3));
+  Term            mod = Deref(ARG3);
 
   if (IsVarTerm(t))
     return (FALSE);
@@ -1852,17 +1836,15 @@ p_is_multifile(void)
 {				/* '$is_multifile'(+S,+Mod)	 */
   PredEntry      *pe;
   Term            t = Deref(ARG1);
-  Term            t2 = Deref(ARG2);
+  Term            mod = Deref(ARG2);
   Int		  out;
-  int		  mod;
 
   if (IsVarTerm(t))
     return (FALSE);
-  if (IsVarTerm(t2))
+  if (IsVarTerm(mod))
     return (FALSE);
-  if (!IsAtomTerm(t2))
+  if (!IsAtomTerm(mod))
     return (FALSE);
-  mod = Yap_LookupModule(t2);
   if (IsAtomTerm(t)) {
     pe = RepPredProp(Yap_GetPredPropByAtom(AtomOfTerm(t), mod));
   } else if (IsApplTerm(t)) {
@@ -1882,9 +1864,8 @@ p_is_log_updatable(void)
 {				/* '$is_dynamic'(+P)	 */
   PredEntry      *pe;
   Term            t = Deref(ARG1);
-  Term            t2 = Deref(ARG2);
   Int             out;
-  SMALLUNSGN      mod = Yap_LookupModule(t2);
+  Term            mod = Deref(ARG2);
 
   if (IsVarTerm(t)) {
     return (FALSE);
@@ -1909,9 +1890,8 @@ p_is_source(void)
 {				/* '$is_dynamic'(+P)	 */
   PredEntry      *pe;
   Term            t = Deref(ARG1);
-  Term            t2 = Deref(ARG2);
+  Term            mod = Deref(ARG2);
   Int             out;
-  SMALLUNSGN      mod = Yap_LookupModule(t2);
 
   if (IsVarTerm(t)) {
     return (FALSE);
@@ -1936,9 +1916,8 @@ p_is_dynamic(void)
 {				/* '$is_dynamic'(+P)	 */
   PredEntry      *pe;
   Term            t = Deref(ARG1);
-  Term            t2 = Deref(ARG2);
+  Term            mod = Deref(ARG2);
   Int             out;
-  SMALLUNSGN      mod = Yap_LookupModule(t2);
 
   if (IsVarTerm(t)) {
     return (FALSE);
@@ -1963,9 +1942,8 @@ p_pred_exists(void)
 {				/* '$pred_exists'(+P,+M)	 */
   PredEntry      *pe;
   Term            t = Deref(ARG1);
-  Term            t2 = Deref(ARG2);
+  Term            mod = Deref(ARG2);
   Int             out;
-  SMALLUNSGN      mod = Yap_LookupModule(t2);
 
   if (IsVarTerm(t)) {
     return (FALSE);
@@ -1992,7 +1970,7 @@ p_set_pred_module(void)
 {				/* '$set_pred_module'(+P,+Mod)	 */
   PredEntry      *pe;
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = CurrentModule;
+  Term            mod = CurrentModule;
 
  restart_set_pred:
   if (IsVarTerm(t)) {
@@ -2011,7 +1989,7 @@ p_set_pred_module(void)
 	Yap_Error(TYPE_ERROR_ATOM,ARG1,"set_pred_module/1");
 	return(FALSE);
       }
-      mod = Yap_LookupModule(tmod);
+      mod = tmod;
       t = ArgOfTerm(2, t);
       goto restart_set_pred;
     }
@@ -2021,10 +1999,7 @@ p_set_pred_module(void)
   if (EndOfPAEntr(pe))
     return FALSE;
   WRITE_LOCK(pe->PRWLock);
-  {
-    SMALLUNSGN mod = Yap_LookupModule(Deref(ARG2));
-    pe->ModuleOfPred = mod;
-  }
+  pe->ModuleOfPred = Deref(ARG2);
   WRITE_UNLOCK(pe->PRWLock);
   return(TRUE);
 }
@@ -2034,20 +2009,18 @@ p_undefined(void)
 {				/* '$undefined'(P,Mod)	 */
   PredEntry      *pe;
   Term            t;
-  Term            t2;
-  SMALLUNSGN      mod;
+  Term            mod;
 
   t = Deref(ARG1);
-  t2 = Deref(ARG2);
-  if (IsVarTerm(t2)) {
+  mod = Deref(ARG2);
+  if (IsVarTerm(mod)) {
     Yap_Error(INSTANTIATION_ERROR,ARG2,"undefined/1");
     return(FALSE);
   }
-  if (!IsAtomTerm(t2)) {
+  if (!IsAtomTerm(mod)) {
     Yap_Error(TYPE_ERROR_ATOM,ARG2,"undefined/1");
     return(FALSE);
   }
-  mod = Yap_LookupModule(t2);
  restart_undefined:
   if (IsVarTerm(t)) {
     Yap_Error(INSTANTIATION_ERROR,ARG1,"undefined/1");
@@ -2068,7 +2041,7 @@ p_undefined(void)
 	Yap_Error(TYPE_ERROR_ATOM,ARG1,"undefined/1");
 	return(FALSE);
       }
-      mod = Yap_LookupModule(tmod);
+      mod = tmod;
       t = ArgOfTerm(2, t);
       goto restart_undefined;
     }
@@ -2101,19 +2074,17 @@ p_kill_dynamic(void)
 {				/* '$kill_dynamic'(P,M)       */
   PredEntry      *pe;
   Term            t;
-  Term            t2;
-  SMALLUNSGN      mod;
+  Term            mod;
 
-  t2 = Deref(ARG2);
-  if (IsVarTerm(t2)) {
+  mod = Deref(ARG2);
+  if (IsVarTerm(mod)) {
     Yap_Error(INSTANTIATION_ERROR,ARG2,"undefined/1");
     return(FALSE);
   }
-  if (!IsAtomTerm(t2)) {
+  if (!IsAtomTerm(mod)) {
     Yap_Error(TYPE_ERROR_ATOM,ARG2,"undefined/1");
     return(FALSE);
   }
-  mod = Yap_LookupModule(t2);
   t = Deref(ARG1);
   if (IsAtomTerm(t)) {
     Atom at = AtomOfTerm(t);
@@ -2654,7 +2625,7 @@ code_in_pred(PredEntry *pp, Atom *pat, UInt *parity, yamop *codeptr) {
 }
 
 static Int
-PredForCode(yamop *codeptr, Atom *pat, UInt *parity, SMALLUNSGN *pmodule) {
+PredForCode(yamop *codeptr, Atom *pat, UInt *parity, Term *pmodule) {
   Int found = 0;
   Int i_table;
 
@@ -2673,7 +2644,7 @@ PredForCode(yamop *codeptr, Atom *pat, UInt *parity, SMALLUNSGN *pmodule) {
 }
 
 Int
-Yap_PredForCode(yamop *codeptr, Atom *pat, UInt *parity, SMALLUNSGN *pmodule) {
+Yap_PredForCode(yamop *codeptr, Atom *pat, UInt *parity, Term *pmodule) {
   return PredForCode(codeptr, pat, parity, pmodule);
 }
 
@@ -2683,7 +2654,7 @@ p_pred_for_code(void) {
   yamop *codeptr;
   Atom at;
   UInt arity;
-  SMALLUNSGN module;
+  Term module;
   Int cl;
   Term t = Deref(ARG1);
 
@@ -2697,12 +2668,13 @@ p_pred_for_code(void) {
     return FALSE;
   }
   cl = PredForCode(codeptr, &at, &arity, &module);
+  if (!module) module = TermProlog;
   if (cl == 0) {
     return(Yap_unify(ARG5,MkIntTerm(0)));
   } else {
     return(Yap_unify(ARG2,MkAtomTerm(at)) &&
 	   Yap_unify(ARG3,MkIntegerTerm(arity)) &&
-	   Yap_unify(ARG4,ModuleName[module]) &&
+	   Yap_unify(ARG4,module) &&
 	   Yap_unify(ARG5,MkIntegerTerm(cl)));
   }
 }
@@ -2742,16 +2714,14 @@ p_is_profiled(void)
 static Int
 p_profile_info(void)
 {
-  Term tmod = Deref(ARG1);
+  Term mod = Deref(ARG1);
   Term tfun = Deref(ARG2);
-  int mod;
   Term out;
   PredEntry *pe;
   Term p[3];
 
-  if (IsVarTerm(tmod) || !IsAtomTerm(tmod))
+  if (IsVarTerm(mod) || !IsAtomTerm(mod))
     return(FALSE);
-  mod = Yap_LookupModule(tmod);
   if (IsVarTerm(tfun)) {
     return(FALSE);
   } else if (IsApplTerm(tfun)) {
@@ -2783,14 +2753,12 @@ p_profile_info(void)
 static Int
 p_profile_reset(void)
 {
-  Term tmod = Deref(ARG1);
+  Term mod = Deref(ARG1);
   Term tfun = Deref(ARG2);
-  int mod;
   PredEntry *pe;
 
-  if (IsVarTerm(tmod) || !IsAtomTerm(tmod))
+  if (IsVarTerm(mod) || !IsAtomTerm(mod))
     return(FALSE);
-  mod = Yap_LookupModule(tmod);
   if (IsVarTerm(tfun)) {
     return(FALSE);
   } else if (IsApplTerm(tfun)) {
@@ -2903,7 +2871,7 @@ p_parent_pred(void)
      We assume a sequence of the form a -> b */
   Atom at;
   UInt arity;
-  SMALLUNSGN module;
+  Term module;
   if (!PredForCode(P_before_spy, &at, &arity, &module)) {
     return(Yap_unify(ARG1, MkIntTerm(0)) &&
 	   Yap_unify(ARG2, MkAtomTerm(AtomMetaCall)) &&
@@ -2920,7 +2888,7 @@ p_system_pred(void)
   PredEntry      *pe;
 
   Term t1 = Deref(ARG1);
-  SMALLUNSGN mod = Yap_LookupModule(Deref(ARG2));
+  Term mod = Deref(ARG2);
 
  restart_system_pred:
   if (IsVarTerm(t1))
@@ -2952,7 +2920,7 @@ p_system_pred(void)
     return (FALSE);
   if (EndOfPAEntr(pe))
     return(FALSE);
-  return(pe->ModuleOfPred == 0 || pe->PredFlags & (UserCPredFlag|CPredFlag|BinaryTestPredFlag|AsmPredFlag|TestPredFlag));
+  return(!pe->ModuleOfPred || pe->PredFlags & (UserCPredFlag|CPredFlag|BinaryTestPredFlag|AsmPredFlag|TestPredFlag));
 }
 
 static Int			/* $system_predicate(P) */
@@ -2961,7 +2929,7 @@ p_hide_predicate(void)
   PredEntry      *pe;
 
   Term t1 = Deref(ARG1);
-  SMALLUNSGN mod = Yap_LookupModule(Deref(ARG2));
+  Term mod = Deref(ARG2);
 
  restart_system_pred:
   if (IsVarTerm(t1))
@@ -3003,7 +2971,7 @@ p_hidden_predicate(void)
   PredEntry      *pe;
 
   Term t1 = Deref(ARG1);
-  SMALLUNSGN mod = Yap_LookupModule(Deref(ARG2));
+  Term mod = Deref(ARG2);
 
  restart_system_pred:
   if (IsVarTerm(t1))
@@ -3039,9 +3007,8 @@ p_hidden_predicate(void)
 }
 
 static PredEntry *
-get_pred(Term t1, Term tmod, char *command)
+get_pred(Term t1, Term mod, char *command)
 {
-  SMALLUNSGN mod = Yap_LookupModule(tmod);
 
  restart_system_pred:
   if (IsVarTerm(t1))
@@ -3366,7 +3333,7 @@ p_nth_clause(void)
     return FALSE;
   }
   /* in case we have to index or to expand code */
-  if (pe->ModuleOfPred != 2) {
+  if (pe->ModuleOfPred != IDB_MODULE) {
     UInt i;
 
     for (i = 1; i <= pe->ArityOfPE; i++) {
@@ -3545,8 +3512,7 @@ static Int
 p_static_pred_statistics(void)
 {
   Term t = Deref(ARG1);
-  Term tmod = Deref(ARG2);
-  SMALLUNSGN      mod = Yap_LookupModule(tmod);
+  Term mod = Deref(ARG2);
   PredEntry      *pe;
 
   if (IsVarTerm(t)) {
diff --git a/C/compiler.c b/C/compiler.c
index b602c74e5..9b259cf3f 100644
--- a/C/compiler.c
+++ b/C/compiler.c
@@ -1145,7 +1145,7 @@ c_goal(Term Goal, int mod, compiler_struct *cglobs)
       longjmp(cglobs->cint.CompilerBotch, 1);
     }
     Goal = ArgOfTerm(2, Goal);
-    mod = Yap_LookupModule(M);
+    mod = M;
   }
   if (IsVarTerm(Goal)) {
     Goal = Yap_MkApplTerm(FunctorCall, 1, &Goal);
diff --git a/C/computils.c b/C/computils.c
index 18dc03aae..91c908e26 100644
--- a/C/computils.c
+++ b/C/computils.c
@@ -74,7 +74,7 @@ Yap_AllocCMem (int size, struct intermediates *cip)
 }
 
 int
-Yap_is_a_test_pred (Term arg, SMALLUNSGN mod)
+Yap_is_a_test_pred (Term arg, Term mod)
 {
   if (IsVarTerm (arg))
     return FALSE;
@@ -373,10 +373,13 @@ ShowOp (char *f, struct PSEUDO *cpc)
 	      PredEntry *p = RepPredProp ((Prop) arg);
 	      Functor f = p->FunctorOfPred;
 	      UInt arity = p->ArityOfPE;
-	      SMALLUNSGN mod = 0;
+	      Term mod;
 
-	      if (p->ModuleOfPred) mod = IntOfTerm(p->ModuleOfPred);
-	      Yap_plwrite (ModuleName[mod], Yap_DebugPutc, 0);
+	      if (p->ModuleOfPred)
+		mod = p->ModuleOfPred;
+	      else
+		mod = TermProlog;
+	      Yap_plwrite (mod, Yap_DebugPutc, 0);
 	      Yap_DebugPutc (Yap_c_error_stream,':');
 	      if (arity == 0)
 		Yap_plwrite (MkAtomTerm ((Atom)f), Yap_DebugPutc, 0);
@@ -391,10 +394,10 @@ ShowOp (char *f, struct PSEUDO *cpc)
 	      PredEntry *p = RepPredProp((Prop) rn);
 	      Functor f = p->FunctorOfPred;
 	      UInt arity = p->ArityOfPE;
-	      SMALLUNSGN mod = 0;
+	      Term mod = TermProlog;
 
-	      if (p->ModuleOfPred) mod = IntOfTerm(p->ModuleOfPred);
-	      Yap_plwrite (ModuleName[mod], Yap_DebugPutc, 0);
+	      if (p->ModuleOfPred) mod = p->ModuleOfPred;
+	      Yap_plwrite (mod, Yap_DebugPutc, 0);
 	      Yap_DebugPutc (Yap_c_error_stream,':');
 	      if (arity == 0)
 		Yap_plwrite (MkAtomTerm ((Atom)f), Yap_DebugPutc, 0);
diff --git a/C/dbase.c b/C/dbase.c
index f08a7c8c7..08f48ebcb 100644
--- a/C/dbase.c
+++ b/C/dbase.c
@@ -186,7 +186,7 @@ STATIC_PROTO(void linkblk,(link_entry *,CELL *,CELL));
 STATIC_PROTO(CELL *linkcells,(CELL *,Int));
 #endif
 STATIC_PROTO(Int cmpclls,(CELL *,CELL *,Int));
-STATIC_PROTO(Prop FindDBProp,(AtomEntry *, int, unsigned int, SMALLUNSGN));
+STATIC_PROTO(Prop FindDBProp,(AtomEntry *, int, unsigned int, Term));
 STATIC_PROTO(CELL  CalcKey, (Term));
 #ifdef COROUTINING
 STATIC_PROTO(CELL  *MkDBTerm, (CELL *, CELL *, CELL *, CELL *, CELL *, CELL *,int *));
@@ -381,7 +381,7 @@ int Yap_DBTrailOverflow(void)
 
 /* get DB entry for ap/arity; */
 static Prop 
-FindDBPropHavingLock(AtomEntry *ae, int CodeDB, unsigned int arity, SMALLUNSGN dbmod)
+FindDBPropHavingLock(AtomEntry *ae, int CodeDB, unsigned int arity, Term dbmod)
 {
   Prop          p0;
   DBProp        p;
@@ -398,7 +398,7 @@ FindDBPropHavingLock(AtomEntry *ae, int CodeDB, unsigned int arity, SMALLUNSGN d
 
 /* get DB entry for ap/arity; */
 static Prop 
-FindDBProp(AtomEntry *ae, int CodeDB, unsigned int arity, SMALLUNSGN dbmod)
+FindDBProp(AtomEntry *ae, int CodeDB, unsigned int arity, Term dbmod)
 {
   Prop out;
 
@@ -2388,7 +2388,10 @@ UnifyDBKey(DBRef DBSP, PropFlags flags, Term t)
   }
   if ((p->KindOfPE & CodeDBBit) && (flags & CodeDBBit)) {
     Term t[2];
-    t[0] = ModuleName[p->ModuleOfDB];
+    if (p->ModuleOfDB)
+      t[0] = p->ModuleOfDB;
+    else
+      t[0] = TermProlog;
     t[1] = t1;
     tf = Yap_MkApplTerm(FunctorModule, 2, t);
   } else if (!(flags & CodeDBBit)) {
@@ -2609,7 +2612,7 @@ new_lu_int_key(Int key)
   }
   fe = Yap_MkFunctor(Yap_FullLookupAtom("$integer"),3);
   WRITE_LOCK(fe->FRWLock);
-  p0 = Yap_NewPredPropByFunctor(fe,2);
+  p0 = Yap_NewPredPropByFunctor(fe,IDB_MODULE);
   p = RepPredProp(p0);
   p->NextOfPE = INT_LU_KEYS[hash_key];
   p->src.IndxId = key;
@@ -2631,15 +2634,15 @@ new_lu_entry(Term t)
     Functor f = FunctorOfTerm(t);
 
     WRITE_LOCK(f->FRWLock);
-    p0 = Yap_NewPredPropByFunctor(f,2);
+    p0 = Yap_NewPredPropByFunctor(f,IDB_MODULE);
   } else if (IsAtomTerm(t)) {
     Atom at = AtomOfTerm(t);
 
     WRITE_LOCK(RepAtom(at)->ARWLock);
-    p0 = Yap_NewPredPropByAtom(at,2);
+    p0 = Yap_NewPredPropByAtom(at,IDB_MODULE);
   } else {
     WRITE_LOCK(FunctorList->FRWLock);
-    p0 = Yap_NewPredPropByFunctor(FunctorList,2);
+    p0 = Yap_NewPredPropByFunctor(FunctorList,IDB_MODULE);
   }
   pe = RepPredProp(p0);
   pe->PredFlags |= LogUpdatePredFlag;
@@ -2696,11 +2699,11 @@ find_lu_entry(Term t)
       Yap_Error(TYPE_ERROR_KEY, t, "while accessing database key");
       return NULL;
     }
-    p = Yap_GetPredPropByFuncInThisModule(FunctorOfTerm(t),2);
+    p = Yap_GetPredPropByFuncInThisModule(FunctorOfTerm(t),IDB_MODULE);
   } else if (IsAtomTerm(t)) {
-    p = Yap_GetPredPropByAtomInThisModule(AtomOfTerm(t),2);
+    p = Yap_GetPredPropByAtomInThisModule(AtomOfTerm(t),IDB_MODULE);
   } else {
-    p = Yap_GetPredPropByFuncInThisModule(FunctorList,2);
+    p = Yap_GetPredPropByFuncInThisModule(FunctorList,IDB_MODULE);
   }
   if (p == NIL) {
     if (UPDATE_MODE == UPDATE_MODE_LOGICAL && !find_entry(t)) {
@@ -2760,7 +2763,7 @@ FetchDBPropFromKey(Term twork, int flag, int new, char *error_mssg)
 {
   Atom At;
   Int arity;
-  SMALLUNSGN dbmod;
+  Term dbmod;
 
   if (flag & MkCode) {
     if (IsVarTerm(twork)) {
@@ -2772,21 +2775,19 @@ FetchDBPropFromKey(Term twork, int flag, int new, char *error_mssg)
       return RepDBProp(NULL);
     } else {
       Functor f = FunctorOfTerm(twork);
-      Term tmod;
       if (f != FunctorModule) {
 	Yap_Error(SYSTEM_ERROR, twork, "missing module");
 	return RepDBProp(NULL);
       }
-      tmod = ArgOfTerm(1, twork);
-      if (IsVarTerm(tmod)) {
+      dbmod = ArgOfTerm(1, twork);
+      if (IsVarTerm(dbmod)) {
 	Yap_Error(INSTANTIATION_ERROR, twork, "var in module");
 	return(RepDBProp(NIL));
       }
-      if (!IsAtomTerm(tmod)) {
+      if (!IsAtomTerm(dbmod)) {
 	Yap_Error(TYPE_ERROR_ATOM, twork, "not atom in module");
 	return(RepDBProp(NIL));
       }
-      dbmod = Yap_LookupModule(tmod);
       twork = ArgOfTerm(2, twork);
     }
   } else {
@@ -4193,7 +4194,7 @@ p_erase_clause(void)
   if (entryref->Flags & StaticMask) {
     if (entryref->Flags & ErasedMask)
       return FALSE;
-    Yap_EraseStaticClause((StaticClause *)entryref, Yap_LookupModule(Deref(ARG2)));
+    Yap_EraseStaticClause((StaticClause *)entryref, Deref(ARG2));
     return TRUE;
   }
   EraseEntry(entryref);
@@ -4446,9 +4447,12 @@ p_instance_module(void)
     if (cl->ClFlags & ErasedMask) {
       return FALSE;
     }
-    return Yap_unify(ARG2, ModuleName[cl->ClPred->ModuleOfPred]);
+    if (cl->ClPred->ModuleOfPred)
+      return Yap_unify(ARG2, cl->ClPred->ModuleOfPred);
+    else
+      return Yap_unify(ARG2, TermProlog);
   } else {
-    return Yap_unify(ARG2, ModuleName[dbr->Parent->ModuleOfDB]);
+    return Yap_unify(ARG2, dbr->Parent->ModuleOfDB);
   }
 }
 
@@ -4920,8 +4924,7 @@ p_install_thread_local(void)
 #if THREADS
   PredEntry      *pe;
   Term            t = Deref(ARG1);
-  Term            t2 = Deref(ARG2);
-  SMALLUNSGN      mod = Yap_LookupModule(t2);
+  Term            mod = Deref(ARG2);
 
   if (IsVarTerm(t)) {
     return (FALSE);
diff --git a/C/errors.c b/C/errors.c
index cbc2804c3..c29a9a34a 100644
--- a/C/errors.c
+++ b/C/errors.c
@@ -107,15 +107,15 @@ DumpActiveGoals (void)
       if (pe->PredFlags & (CompiledPredFlag | DynamicPredFlag | FastPredFlag))
 	{
 	  Functor f;
-	  SMALLUNSGN mod = 0;
+	  Term mod = TermProlog;
 
 	  f = pe->FunctorOfPred;
 	  if (pe->KindOfPE && hidden (NameOfFunctor (f)))
 	    goto next;
 	  if (first++ == 1)
 	    fprintf(stderr,"Active ancestors:\n");
-	  if (pe->ModuleOfPred) mod = IntOfTerm(pe->ModuleOfPred);
-	  Yap_plwrite (ModuleName[mod], Yap_DebugPutc, 0);
+	  if (pe->ModuleOfPred) mod = pe->ModuleOfPred;
+	  Yap_plwrite (mod, Yap_DebugPutc, 0);
 	  Yap_DebugPutc (Yap_c_error_stream,':');
 	  if (pe->ArityOfPE == 0) {
 	    Yap_plwrite (MkAtomTerm ((Atom)f), Yap_DebugPutc, 0);
@@ -162,11 +162,13 @@ DumpActiveGoals (void)
       READ_LOCK(pe->PRWLock);
       {
 	Functor f;
-	SMALLUNSGN mod = 0;
+	Term mod = PROLOG_MODULE;
 
 	f = pe->FunctorOfPred;
-	if (pe->ModuleOfPred) mod = IntOfTerm(pe->ModuleOfPred);
-	Yap_plwrite (ModuleName[mod], Yap_DebugPutc, 0);
+	if (pe->ModuleOfPred)
+	  mod = pe->ModuleOfPred;
+	else mod = TermProlog;
+	Yap_plwrite (mod, Yap_DebugPutc, 0);
 	Yap_DebugPutc (Yap_c_error_stream,':');
 	if (pe->ArityOfPE == 0) {
 	  Yap_plwrite (MkAtomTerm (NameOfFunctor(f)), Yap_DebugPutc, 0);
@@ -194,7 +196,7 @@ detect_bug_location(yamop *yap_pc, char *tp, int psize)
 {
   Atom pred_name;
   UInt pred_arity;
-  SMALLUNSGN pred_module;
+  Term pred_module;
   Int cl;
 
   if ((cl = Yap_PredForCode(yap_pc, &pred_name, &pred_arity, &pred_module))
@@ -211,22 +213,18 @@ detect_bug_location(yamop *yap_pc, char *tp, int psize)
     /* don't give info on system predicates */
 #if   HAVE_SNPRINTF
 #if SHORT_INTS
-    snprintf(tp, psize, "%s:%s/%ld",
-	     RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+    snprintf(tp, psize, "prolog:%s/%ld",
 	     RepAtom(pred_name)->StrOfAE, pred_arity);
 #else
-    snprintf(tp, psize, "%s:%s/%d",
-	     RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+    snprintf(tp, psize, "prolog:%s/%d",
 	     RepAtom(pred_name)->StrOfAE, pred_arity);
 #endif
 #else
 #if SHORT_INTS
-    sprintf(tp, "in %s:%s/%ld",
-	    RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+    sprintf(tp, "in prolog:%s/%ld",
 	    RepAtom(pred_name)->StrOfAE, pred_arity);
 #else
-    sprintf(tp, "in %s:%s/%d",
-	    RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+    sprintf(tp, "in prolog:%s/%d",
 	    RepAtom(pred_name)->StrOfAE, pred_arity);
 #endif
 #endif
@@ -234,21 +232,21 @@ detect_bug_location(yamop *yap_pc, char *tp, int psize)
 #if   HAVE_SNPRINTF
 #if SHORT_INTS
     snprintf(tp, psize, "indexing code of %s:%s/%ld",
-	     RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+	     RepAtom(AtomOfTerm(pred_module))->StrOfAE,
 	     RepAtom(pred_name)->StrOfAE, pred_arity);
 #else
     snprintf(tp, psize, "indexing code of %s:%s/%d",
-	     RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+	     RepAtom(AtomOfTerm(pred_module))->StrOfAE,
 	     RepAtom(pred_name)->StrOfAE, pred_arity);
 #endif
 #else
 #if SHORT_INTS
     sprintf(tp, "indexing code of %s:%s/%ld",
-	    RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+	    RepAtom(AtomOfTerm(pred_module))->StrOfAE,
 	    RepAtom(pred_name)->StrOfAE, pred_arity);
 #else 
     sprintf(tp, "indexing code of %s:%s/%d",
-	    RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+	    RepAtom(AtomOfTerm(pred_module))->StrOfAE,
 	    RepAtom(pred_name)->StrOfAE, pred_arity);
 #endif
 #endif
@@ -256,21 +254,21 @@ detect_bug_location(yamop *yap_pc, char *tp, int psize)
 #if   HAVE_SNPRINTF
 #if SHORT_INTS
     snprintf(tp, psize, "clause %ld of %s:%s/%ld", cl,
-	     RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+	     RepAtom(AtomOfTerm(pred_module))->StrOfAE,
 	     RepAtom(pred_name)->StrOfAE, pred_arity);
 #else
     snprintf(tp, psize, "clause %d of %s:%s/%d", cl,
-	     RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+	     RepAtom(AtomOfTerm(pred_module))->StrOfAE,
 	     RepAtom(pred_name)->StrOfAE, pred_arity);
 #endif
 #else
 #if SHORT_INTS
     sprintf(tp, "clause %ld of %s:%s/%ld", cl,
-	    RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+	    RepAtom(AtomOfTerm(pred_module))->StrOfAE,
 	    RepAtom(pred_name)->StrOfAE, pred_arity);
 #else
     sprintf(tp, "clause %d of %s:%s/%d", cl,
-	    RepAtom(AtomOfTerm(ModuleName[pred_module]))->StrOfAE,
+	    RepAtom(AtomOfTerm(pred_module))->StrOfAE,
 	    RepAtom(pred_name)->StrOfAE, pred_arity);
 #endif
 #endif
diff --git a/C/exec.c b/C/exec.c
index 6a12745aa..12a37f579 100644
--- a/C/exec.c
+++ b/C/exec.c
@@ -22,7 +22,7 @@ static char     SccsId[] = "@(#)cdmgr.c	1.1 05/02/98";
 #include "yapio.h"
 
 STATIC_PROTO(Int  CallPredicate, (PredEntry *, choiceptr));
-STATIC_PROTO(Int  EnterCreepMode, (Term, SMALLUNSGN));
+STATIC_PROTO(Int  EnterCreepMode, (Term, Term));
 STATIC_PROTO(Int  CallClause, (PredEntry *, Int));
 STATIC_PROTO(Int  p_save_cp, (void));
 STATIC_PROTO(Int  p_execute, (void));
@@ -74,25 +74,25 @@ CallPredicate(PredEntry *pen, choiceptr cut_pt) {
 }
 
 inline static Int
-CallMetaCall(SMALLUNSGN mod) {
+CallMetaCall(Term mod) {
   ARG2 = cp_as_integer(B); /* p_save_cp */
   ARG3 = ARG1;
-  ARG4 = ModuleName[mod];
+  ARG4 = mod;
   return (CallPredicate(PredMetaCall, B));
 }
 
 Term
-Yap_ExecuteCallMetaCall(SMALLUNSGN mod) {
+Yap_ExecuteCallMetaCall(Term mod) {
   Term ts[4];
   ts[0] = ARG1;
   ts[1] = cp_as_integer(B); /* p_save_cp */
   ts[2] = ARG1;
-  ts[3] = ModuleName[mod];
+  ts[3] = mod;
   return(Yap_MkApplTerm(PredMetaCall->FunctorOfPred,4,ts));
 }
 
 static Int
-CallError(yap_error_number err, SMALLUNSGN mod)
+CallError(yap_error_number err, Term mod)
 {
   if (yap_flags[LANGUAGE_MODE_FLAG] == 1) {
     return(CallMetaCall(mod));
@@ -213,7 +213,7 @@ p_save_cp(void)
 }
 
 inline static Int
-do_execute(Term t, SMALLUNSGN mod)
+do_execute(Term t, Term mod)
 {
   if (ActiveSignals) {
     return(EnterCreepMode(t, mod));
@@ -242,7 +242,7 @@ do_execute(Term t, SMALLUNSGN mod)
       if (f == FunctorModule) {
 	Term tmod = ArgOfTerm(1,t);
 	if (!IsVarTerm(tmod) && IsAtomTerm(tmod)) {
-	  mod = Yap_LookupModule(tmod);
+	  mod = tmod;
 	  t = ArgOfTerm(2,t);
 	  goto restart_exec;
 	}
@@ -287,7 +287,7 @@ do_execute(Term t, SMALLUNSGN mod)
 }
 
 static Int
-EnterCreepMode(Term t, SMALLUNSGN mod) {
+EnterCreepMode(Term t, Term mod) {
   PredEntry *PredCreep;
 
   if (ActiveSignals & YAP_CDOVF_SIGNAL) {
@@ -300,7 +300,11 @@ EnterCreepMode(Term t, SMALLUNSGN mod) {
     }
   }
   PredCreep = RepPredProp(PredPropByFunc(FunctorCreep,1));
-  ARG1 = MkPairTerm(ModuleName[mod],ARG1);
+  if (mod) {
+    ARG1 = MkPairTerm(mod,ARG1);
+  } else {
+    ARG1 = MkPairTerm(TermProlog,ARG1);
+  }
   LOCK(SignalLock);
   CreepFlag = CalculateStackGap();
   UNLOCK(SignalLock);
@@ -325,10 +329,9 @@ static Int
 p_execute0(void)
 {				/* '$execute0'(Goal,Mod)	 */
   Term            t = Deref(ARG1);
-  Term            tmod = Deref(ARG2);
+  Term            mod = Deref(ARG2);
   unsigned int    arity;
   Prop            pe;
-  SMALLUNSGN      mod = Yap_LookupModule(tmod);
 
  restart_exec:
   if (IsVarTerm(t)) {
@@ -347,7 +350,7 @@ p_execute0(void)
     if (f == FunctorModule) {
       Term tmod = ArgOfTerm(1,t);
       if (!IsVarTerm(tmod) && IsAtomTerm(tmod)) {
-	mod = Yap_LookupModule(tmod);
+	mod = tmod;
 	t = ArgOfTerm(2,t);
 	goto restart_exec;
       }
@@ -382,7 +385,7 @@ static Int
 p_execute_0(void)
 {				/* '$execute_0'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG2));
+  Term            mod = Deref(ARG2);
   Prop            pe;
 
   if (IsAtomTerm(t)) {
@@ -419,7 +422,7 @@ static Int
 p_execute_1(void)
 {				/* '$execute_0'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG3));
+  Term            mod = Deref(ARG3);
   Prop            pe;
 
   if (!IsAtomTerm(t)) {
@@ -465,7 +468,7 @@ static Int
 p_execute_2(void)
 {				/* '$execute_2'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG4));
+  Term            mod = Deref(ARG4);
   Prop            pe;
 
   if (IsAtomTerm(t)) {
@@ -510,7 +513,7 @@ static Int
 p_execute_3(void)
 {				/* '$execute_3'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG5));
+  Term            mod = Deref(ARG5);
   Prop            pe;
 
   if (!IsAtomTerm(t)) {
@@ -562,7 +565,7 @@ static Int
 p_execute_4(void)
 {				/* '$execute_4'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG6));
+  Term            mod = Deref(ARG6);
   Prop            pe;
 
   if (IsAtomTerm(t)) {
@@ -613,7 +616,7 @@ static Int
 p_execute_5(void)
 {				/* '$execute_5'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG7));
+  Term            mod = Deref(ARG7);
   Prop            pe;
 
   if (IsAtomTerm(t)) {
@@ -667,7 +670,7 @@ static Int
 p_execute_6(void)
 {				/* '$execute_6'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG8));
+  Term            mod = Deref(ARG8);
   Prop            pe;
 
   if (IsAtomTerm(t)) {
@@ -724,7 +727,7 @@ static Int
 p_execute_7(void)
 {				/* '$execute_7'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG9));
+  Term            mod = Deref(ARG9);
   Prop            pe;
 
   if (IsAtomTerm(t)) {
@@ -784,7 +787,7 @@ static Int
 p_execute_8(void)
 {				/* '$execute_8'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG10));
+  Term            mod = Deref(ARG10);
   Prop            pe;
 
   if (IsAtomTerm(t)) {
@@ -847,7 +850,7 @@ static Int
 p_execute_9(void)
 {				/* '$execute_9'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG11));
+  Term            mod = Deref(ARG11);
   Prop            pe;
 
   if (IsAtomTerm(t)) {
@@ -913,7 +916,7 @@ static Int
 p_execute_10(void)
 {				/* '$execute_10'(Goal)	 */
   Term            t = Deref(ARG1);
-  SMALLUNSGN      mod = Yap_LookupModule(Deref(ARG12));
+  Term            mod = Deref(ARG12);
   Prop            pe;
 
   if (IsAtomTerm(t)) {
@@ -1003,11 +1006,10 @@ p_pred_goal_expansion_on(void) {
 static Int 
 p_at_execute(void)
 {				/* '$execute'(Goal,ClauseNumber) */
-  Term            t = Deref(ARG1), tmod = Deref(ARG2), t2 = Deref(ARG3);
+  Term            t = Deref(ARG1), mod = Deref(ARG2), t2 = Deref(ARG3);
   unsigned	  int arity;
   Prop            pe;
   Atom            a;
-  SMALLUNSGN      mod = Yap_LookupModule(tmod);
 
  restart_exec:
   if (IsAtomTerm(t)) {
@@ -1024,7 +1026,7 @@ p_at_execute(void)
     if (f == FunctorModule) {
       Term tmod = ArgOfTerm(1,t);
       if (!IsVarTerm(tmod) && IsAtomTerm(tmod)) {
-	mod = Yap_LookupModule(tmod);
+	mod = tmod;
 	t = ArgOfTerm(2,t);
 	goto restart_exec;
       }
@@ -1176,7 +1178,7 @@ Yap_exec_absmi(int top)
 
 
 Int
-Yap_execute_goal(Term t, int nargs, SMALLUNSGN mod)
+Yap_execute_goal(Term t, int nargs, Term mod)
 {
   Int             out;
   yamop        *CodeAdr;
@@ -1307,7 +1309,7 @@ Yap_RunTopGoal(Term t)
   PredEntry *ppe;
   CELL *pt;
   UInt arity;
-  SMALLUNSGN mod = CurrentModule;
+  Term mod = CurrentModule;
   int goal_out = 0;
 
  restart_runtopgoal:
@@ -1326,7 +1328,7 @@ Yap_RunTopGoal(Term t)
     if (f == FunctorModule) {
       Term tmod = ArgOfTerm(1,t);
       if (!IsVarTerm(tmod) && IsAtomTerm(tmod)) {
-	mod = Yap_LookupModule(tmod);
+	mod = tmod;
 	t = ArgOfTerm(2,t);
 	goto restart_runtopgoal;
       }
@@ -1531,7 +1533,7 @@ p_jump_env(void) {
 static Int
 p_generate_pred_info(void) {
   ARG1 = ARG3 = ENV[-EnvSizeInCells-1];
-  ARG4 = ModuleName[IntOfTerm(ENV[-EnvSizeInCells-3])];
+  ARG4 = ENV[-EnvSizeInCells-3];
   ARG2 = cp_as_integer((choiceptr)ENV[E_CB]);
   return TRUE;
 }
diff --git a/C/heapgc.c b/C/heapgc.c
index 772b8ebf5..304439ec2 100644
--- a/C/heapgc.c
+++ b/C/heapgc.c
@@ -1473,7 +1473,7 @@ mark_choicepoints(register choiceptr gc_B, tr_fr_ptr saved_TR, int very_verbose)
 	{
 	  Atom at;
 	  UInt arity;
-	  SMALLUNSGN mod;
+	  Term mod;
 	  if (Yap_PredForCode(gc_B->cp_ap, &at, &arity, &mod)) {
 	    if (arity) 
 	      fprintf(Yap_stderr,"[GC]       %s/%ld marked %ld (%s)\n", RepAtom(at)->StrOfAE, (long int)arity, total_marked, op_names[opnum]);
diff --git a/C/index.c b/C/index.c
index f1b2c56af..3a0fb633b 100644
--- a/C/index.c
+++ b/C/index.c
@@ -1943,7 +1943,7 @@ static void
 add_arg_info(ClauseDef *clause, PredEntry *ap, UInt argno)
 {
   yamop *cl;
-  if (ap->ModuleOfPred == 2) {
+  if (ap->ModuleOfPred == IDB_MODULE) {
     cl = clause->Code;
   } else {
     cl = clause->u.WorkPC;
@@ -2179,7 +2179,7 @@ skip_to_arg(ClauseDef *clause, PredEntry *ap, UInt argno, int at_point)
 {
   yamop *cl;
   int done = FALSE;
-  if (ap->ModuleOfPred == 2) {
+  if (ap->ModuleOfPred == IDB_MODULE) {
     return;
   } else {
     cl = clause->CurrentCode;
@@ -3075,7 +3075,7 @@ do_index(ClauseDef *min, ClauseDef* max, struct intermediates *cint, UInt argno,
   ngroups = groups_in(min, max, group);
   if (IsVarTerm(t) &&
       max - min > 2 &&
-      ap->ModuleOfPred != 2) {
+      ap->ModuleOfPred != IDB_MODULE) {
     lablx = new_label();
     Yap_emit(label_op, lablx, Zero, cint);
     while (IsVarTerm(t)) {
@@ -4181,12 +4181,13 @@ ExpandIndex(PredEntry *ap) {
   Yap_Error_Size = 0;
 #ifdef DEBUG
   if (Yap_Option['i' - 'a' + 1]) {
-    Term tmod = ModuleName[ap->ModuleOfPred];
+    Term tmod = ap->ModuleOfPred;
+    if (!tmod) tmod = TermProlog;
     Yap_DebugPutc(Yap_c_error_stream,'>');
     Yap_DebugPutc(Yap_c_error_stream,'\t');
     Yap_plwrite(tmod, Yap_DebugPutc, 0);
     Yap_DebugPutc(Yap_c_error_stream,':');
-    if (ap->ModuleOfPred == 2) {
+    if (ap->ModuleOfPred == IDB_MODULE) {
       Term t = Deref(ARG1);
       if (IsAtomTerm(t)) {
 	Yap_plwrite(t, Yap_DebugPutc, 0);
@@ -5596,12 +5597,13 @@ Yap_AddClauseToIndex(PredEntry *ap, yamop *beg, int first) {
   Yap_ErrorMessage = NULL;
 #ifdef DEBUG
   if (Yap_Option['i' - 'a' + 1]) {
-    Term tmod = ModuleName[ap->ModuleOfPred];
+    Term tmod = ap->ModuleOfPred;
+    if (!tmod) tmod = TermProlog;
     Yap_DebugPutc(Yap_c_error_stream,'+');
     Yap_DebugPutc(Yap_c_error_stream,'\t');
     Yap_plwrite(tmod, Yap_DebugPutc, 0);
     Yap_DebugPutc(Yap_c_error_stream,':');
-    if (ap->ModuleOfPred == 2) {
+    if (ap->ModuleOfPred == IDB_MODULE) {
       Term t = Deref(ARG1);
       if (IsAtomTerm(t)) {
 	Yap_plwrite(t, Yap_DebugPutc, 0);
@@ -6101,13 +6103,14 @@ Yap_RemoveClauseFromIndex(PredEntry *ap, yamop *beg) {
   Yap_ErrorMessage = NULL;
 #ifdef DEBUG
   if (Yap_Option['i' - 'a' + 1]) {
-    Term tmod = ModuleName[ap->ModuleOfPred];
+    Term tmod = ap->ModuleOfPred;
 
+    if (!tmod) tmod = TermProlog;
     Yap_DebugPutc(Yap_c_error_stream,'-');
     Yap_DebugPutc(Yap_c_error_stream,'\t');
     Yap_plwrite(tmod, Yap_DebugPutc, 0);
     Yap_DebugPutc(Yap_c_error_stream,':');
-    if (ap->ModuleOfPred != 2) {
+    if (ap->ModuleOfPred != IDB_MODULE) {
       if (ap->ArityOfPE == 0) {
 	Atom At = (Atom)ap->FunctorOfPred;
 	Yap_plwrite(MkAtomTerm(At), Yap_DebugPutc, 0);
@@ -6248,7 +6251,7 @@ Yap_FollowIndexingCode(PredEntry *ap, yamop *ipc, Term t1, Term tb, Term tr, yam
   yamop **jlbl = NULL;
   int lu_pred = ap->PredFlags & LogUpdatePredFlag;
 
-  if (ap->ModuleOfPred != 2) {
+  if (ap->ModuleOfPred != IDB_MODULE) {
     if (ap->ArityOfPE) {
       CELL *tar = RepAppl(t1);
       UInt i;
@@ -6623,7 +6626,7 @@ Yap_NthClause(PredEntry *ap, Int ncls)
   else if (ncls < 0)
     return NULL;
   
-  if (ap->ModuleOfPred != 2) {
+  if (ap->ModuleOfPred != IDB_MODULE) {
     if (ap->ArityOfPE) {
       UInt i;
 
diff --git a/C/init.c b/C/init.c
index 6a4709df4..814bc6f41 100644
--- a/C/init.c
+++ b/C/init.c
@@ -495,10 +495,7 @@ Yap_InitCPred(char *Name, unsigned long int Arity, CPredicate code, int flags)
   }
   p_code->opc = Yap_opcode(_procceed);
   pe->OpcodeOfPred = pe->CodeOfPred->opc;
-  { 
-    Term mod = CurrentModule;
-    pe->ModuleOfPred = mod;
-  }
+  pe->ModuleOfPred = CurrentModule;
 }
 
 void 
@@ -716,6 +713,12 @@ InitCodes(void)
   Functor
     FunctorThrow;
 
+  heap_regs->user_module = MkAtomTerm(Yap_LookupAtom("user"));
+  heap_regs->idb_module = MkAtomTerm(Yap_LookupAtom("idb"));
+  heap_regs->attributes_module = MkAtomTerm(Yap_LookupAtom("attributes"));
+  heap_regs->charsio_module = MkAtomTerm(Yap_LookupAtom("charsio"));
+  heap_regs->terms_module = MkAtomTerm(Yap_LookupAtom("terms"));
+  Yap_InitModules();
 #ifdef YAPOR
   heap_regs->seq_def = TRUE;
   heap_regs->getworkfirsttimecode.opc = Yap_opcode(_getwork_first_time);
@@ -1006,26 +1009,26 @@ InitCodes(void)
   heap_regs->env_for_yes_code.p =
     heap_regs->env_for_yes_code.p0 =
     RepPredProp(PredPropByAtom(heap_regs->atom_true,0));
-  heap_regs->pred_meta_call = RepPredProp(PredPropByFunc(Yap_MkFunctor(heap_regs->atom_meta_call,4),0));
-  heap_regs->pred_dollar_catch = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$catch"),3),0));
-  heap_regs->pred_recorded_with_key = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$recorded_with_key"),3),0));
-  heap_regs->pred_log_upd_clause = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$do_log_upd_clause"),5),0));
-  heap_regs->pred_log_upd_clause0 = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$do_log_upd_clause"),4),0));
-  heap_regs->pred_static_clause = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$do_static_clause"),5),0));
-  heap_regs->pred_throw = RepPredProp(PredPropByFunc(FunctorThrow,0));
-  heap_regs->pred_handle_throw = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$handle_throw"),3),0));
-  heap_regs->pred_goal_expansion = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_LookupAtom("goal_expansion"),3),1));
+  heap_regs->pred_meta_call = RepPredProp(PredPropByFunc(Yap_MkFunctor(heap_regs->atom_meta_call,4),PROLOG_MODULE));
+  heap_regs->pred_dollar_catch = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$catch"),3),PROLOG_MODULE));
+  heap_regs->pred_recorded_with_key = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$recorded_with_key"),3),PROLOG_MODULE));
+  heap_regs->pred_log_upd_clause = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$do_log_upd_clause"),5),PROLOG_MODULE));
+  heap_regs->pred_log_upd_clause0 = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$do_log_upd_clause"),4),PROLOG_MODULE));
+  heap_regs->pred_static_clause = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$do_static_clause"),5),PROLOG_MODULE));
+  heap_regs->pred_throw = RepPredProp(PredPropByFunc(FunctorThrow,PROLOG_MODULE));
+  heap_regs->pred_handle_throw = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_FullLookupAtom("$handle_throw"),3),PROLOG_MODULE));
+  heap_regs->pred_goal_expansion = RepPredProp(PredPropByFunc(Yap_MkFunctor(Yap_LookupAtom("goal_expansion"),3),USER_MODULE));
   heap_regs->env_for_trustfail_code.p =
     heap_regs->env_for_trustfail_code.p0 =
-    RepPredProp(PredPropByAtom(heap_regs->atom_false,0));
+    RepPredProp(PredPropByAtom(heap_regs->atom_false,PROLOG_MODULE));
   {
     /* make sure we know about the module predicate */
-    PredEntry *modp = RepPredProp(PredPropByFunc(heap_regs->functor_module,0));
+    PredEntry *modp = RepPredProp(PredPropByFunc(heap_regs->functor_module,PROLOG_MODULE));
     modp->PredFlags |= MetaPredFlag;
   }
 #ifdef YAPOR
-  heap_regs->getworkcode.u.ld.p = RepPredProp(PredPropByAtom(Yap_FullLookupAtom("$getwork"), 0));
-  heap_regs->getworkcode_seq.u.ld.p = RepPredProp(PredPropByAtom(Yap_FullLookupAtom("$getwork_seq"), 0));
+  heap_regs->getworkcode.u.ld.p = RepPredProp(PredPropByAtom(Yap_FullLookupAtom("$getwork"), PROLOG_MODULE));
+  heap_regs->getworkcode_seq.u.ld.p = RepPredProp(PredPropByAtom(Yap_FullLookupAtom("$getwork_seq"), PROLOG_MODULE));
 #endif
   heap_regs->db_erased_marker =
     (DBRef)Yap_AllocCodeSpace(sizeof(DBStruct));
@@ -1181,7 +1184,6 @@ Yap_InitWorkspace(int Heap,
 #else
   Yap_InitAbsmi();
 #endif
-  Yap_InitModules();
   InitCodes();
   InitOps();
   InitDebug();
diff --git a/C/load_foreign.c b/C/load_foreign.c
index 4bd5a86a0..38d8d1137 100644
--- a/C/load_foreign.c
+++ b/C/load_foreign.c
@@ -118,7 +118,7 @@ void
 Yap_ReOpenLoadForeign(void)
 {
   ForeignObj *f_code = ForeignCodeLoaded;
-  SMALLUNSGN OldModule = CurrentModule;
+  Term OldModule = CurrentModule;
   YapInitProc InitProc = NULL;
 
   while (f_code != NULL) {
diff --git a/C/modules.c b/C/modules.c
index 31ef54c8e..fe5b0bfb8 100644
--- a/C/modules.c
+++ b/C/modules.c
@@ -27,10 +27,9 @@ STATIC_PROTO(Int p_current_module1, (void));
 
 #define ByteAdr(X) ((char *) &(X))
 Term 
-Yap_Module_Name(CODEADDR cap)
+Yap_Module_Name(PredEntry *ap)
 {
-  PredEntry      *ap = (PredEntry *)cap;
-
+  Term mod;
   if (!ap->ModuleOfPred)
     /* If the system predicate is a metacall I should return the
        module for the metacall, which I will suppose has to be
@@ -39,20 +38,22 @@ Yap_Module_Name(CODEADDR cap)
        So I will return the current module in case the system
        predicate is a meta-call. Otherwise it will still work.
     */
-    return(ModuleName[CurrentModule]);
+    mod =  CurrentModule;
   else {
-    return (ModuleName[ap->ModuleOfPred]);
+    mod = ap->ModuleOfPred;
   }
+  if (mod) return mod;
+  return TermProlog;
 }
 
-static SMALLUNSGN 
+static Term 
 LookupModule(Term a)
 {
   unsigned int             i;
 
   for (i = 0; i < NoOfModules; ++i) {
     if (ModuleName[i] == a) {       
-      return (i);
+      return i;
     }
   }
   ModuleName[i = NoOfModules++] = a;
@@ -62,10 +63,18 @@ LookupModule(Term a)
   return (i);
 }
 
-SMALLUNSGN 
-Yap_LookupModule(Term a)
+struct pred_entry *
+Yap_ModulePred(Term mod)
 {
-  return(LookupModule(a));
+  return ModulePred[LookupModule(mod)];
+}
+
+void
+Yap_NewModulePred(Term mod, struct pred_entry *ap)
+{
+  Term imod =  LookupModule(mod);
+  ap->NextPredOfModule = ModulePred[imod];
+  ModulePred[imod] = ap;
 }
 
 static Int 
@@ -73,44 +82,40 @@ p_current_module(void)
 {				/* $current_module(Old,New)		 */
   Term            t;
 	
-  if (!Yap_unify_constant(ARG1, ModuleName[CurrentModule]))
-    return (0);
+  if (CurrentModule) {
+    if(!Yap_unify_constant(ARG1, CurrentModule))
+      return FALSE;
+  } else {
+    if (!Yap_unify_constant(ARG1, TermProlog))
+      return FALSE;
+  }
   t = Deref(ARG2);
   if (IsVarTerm(t) || !IsAtomTerm(t))
-    return (0);
-  CurrentModule = LookupModule(t);
+    return FALSE;
+  if (t == TermProlog) {
+    CurrentModule = 0;
+  } else {
+    CurrentModule = t;
+    LookupModule(CurrentModule);
+  }
   return (TRUE);
 }
 
 static Int
 p_current_module1(void)
 {				/* $current_module(Old)		 */
-  if (!Yap_unify_constant(ARG1, ModuleName[CurrentModule]))
-    return (0);
-  return (1);
+  if (CurrentModule)
+    return Yap_unify_constant(ARG1, CurrentModule);
+  return Yap_unify_constant(ARG1, TermProlog);
 }
 
 static Int
 p_change_module(void)
 {				/* $change_module(New)		 */
-  SMALLUNSGN mod = LookupModule(Deref(ARG1));
+  Term mod = Deref(ARG1);
+  LookupModule(mod);
   CurrentModule = mod;
-  return (TRUE);
-}
-
-static Int
-p_module_number(void)
-{				/* $module_number(Mod,Num)		 */
-  Term tname = Deref(ARG1);
-  Term t;
-  if (IsVarTerm(tname)) {
-    return(Yap_unify(tname, ModuleName[IntOfTerm(Deref(ARG2))]));
-  } else {
-    t = MkIntTerm(LookupModule(Deref(ARG1)));
-    Yap_unify(t,ARG2);
-    ARG2 = t;
-  }
-  return(TRUE);
+  return TRUE;
 }
 
 static Int 
@@ -139,7 +144,6 @@ Yap_InitModulesC(void)
   Yap_InitCPred("$current_module", 2, p_current_module, SafePredFlag|SyncPredFlag);
   Yap_InitCPred("$current_module", 1, p_current_module1, SafePredFlag|SyncPredFlag);
   Yap_InitCPred("$change_module", 1, p_change_module, SafePredFlag|SyncPredFlag);
-  Yap_InitCPred("$module_number", 2, p_module_number, SafePredFlag);
   Yap_InitCPredBack("$all_current_modules", 1, 1, init_current_module, cont_current_module,
 		SafePredFlag|SyncPredFlag);
 }
@@ -148,18 +152,18 @@ Yap_InitModulesC(void)
 void 
 Yap_InitModules(void)
 {
-  ModuleName[PROLOG_MODULE] =
-    MkAtomTerm(Yap_LookupAtom("prolog"));
-  ModuleName[USER_MODULE] =
-    MkAtomTerm(Yap_LookupAtom("user"));
-  ModuleName[IDB_MODULE] =
-    MkAtomTerm(Yap_LookupAtom("idb"));
-  ModuleName[ATTRIBUTES_MODULE] =
-    MkAtomTerm(Yap_LookupAtom("attributes"));
-  ModuleName[CHARSIO_MODULE] =
-    MkAtomTerm(Yap_LookupAtom("charsio"));
-  ModuleName[TERMS_MODULE] =
-    MkAtomTerm(Yap_LookupAtom("terms"));
+  ModuleName[0] =
+    TermProlog;
+  ModuleName[1] = 
+    USER_MODULE;
+  ModuleName[2] =
+    IDB_MODULE;
+  ModuleName[3] =
+    ATTRIBUTES_MODULE;
+  ModuleName[4] =
+    CHARSIO_MODULE;
+  ModuleName[5] =
+    TERMS_MODULE;
   NoOfModules = 6;
-  CurrentModule = 0;
+  CurrentModule = PROLOG_MODULE;
 }
diff --git a/C/stdpreds.c b/C/stdpreds.c
index bc772d636..413af7116 100644
--- a/C/stdpreds.c
+++ b/C/stdpreds.c
@@ -302,13 +302,13 @@ showprofres(int tipo) {
     if (calls) {
       if (myp->ArityOfPE) {
 	printf("%s:%s/%d -> %uld\n",
-	       RepAtom(AtomOfTerm(ModuleName[myp->ModuleOfPred]))->StrOfAE,
+	       RepAtom(AtomOfTerm(myp->ModuleOfPred))->StrOfAE,
 	       RepAtom(NameOfFunctor(myp->FunctorOfPred))->StrOfAE,
 	       myp->ArityOfPE,
 	       calls);
       } else {
 	printf("%s:%s -> %uld\n",
-	       RepAtom(AtomOfTerm(ModuleName[myp->ModuleOfPred]))->StrOfAE,
+	       RepAtom(AtomOfTerm(myp->ModuleOfPred))->StrOfAE,
 	       RepAtom((Atom)(myp->FunctorOfPred))->StrOfAE,
 	       calls);
       }
@@ -1742,7 +1742,7 @@ cont_current_predicate(void)
   EXTRA_CBACK_ARG(3,1) = (CELL)MkIntegerTerm((Int)(pp->NextPredOfModule));
   if (pp->FunctorOfPred == FunctorModule)
     return(FALSE);
-  if (pp->ModuleOfPred != 2) {
+  if (pp->ModuleOfPred != IDB_MODULE) {
     Arity = pp->ArityOfPE;
     if (Arity)
       name = MkAtomTerm(NameOfFunctor(pp->FunctorOfPred));
@@ -1771,7 +1771,7 @@ init_current_predicate(void)
   Term t1 = Deref(ARG1);
 
   if (IsVarTerm(t1) || !IsAtomTerm(t1)) cut_fail();
-  EXTRA_CBACK_ARG(3,1) = MkIntegerTerm((Int)ModulePred[Yap_LookupModule(t1)]);
+  EXTRA_CBACK_ARG(3,1) = t1;
   return (cont_current_predicate());
 }
 
@@ -1779,7 +1779,7 @@ static Int
 cont_current_predicate_for_atom(void)
 {
   Prop pf = (Prop)IntegerOfTerm(EXTRA_CBACK_ARG(3,1));
-  SMALLUNSGN mod = Yap_LookupModule(Deref(ARG2));
+  Term mod = Deref(ARG2);
 
   while (pf != NIL) {
     FunctorEntry *pp = RepFunctorProp(pf);
@@ -1993,15 +1993,11 @@ p_flags(void)
   PredEntry      *pe;
   Int             newFl;
   Term t1 = Deref(ARG1);
-  Term t2 = Deref(ARG2);
-  int mod;
+  Term mod = Deref(ARG2);
 
-  if (IsVarTerm(t1))
-    return (FALSE);
-  if (!IsAtomTerm(t2)) {
+  if (IsVarTerm(mod) || !IsAtomTerm(mod)) {
     return(FALSE);
   }
-  mod = Yap_LookupModule(t2);
   if (IsVarTerm(t1))
     return (FALSE);
   if (IsAtomTerm(t1)) {
diff --git a/C/tracer.c b/C/tracer.c
index 62080473c..2e3ddab92 100644
--- a/C/tracer.c
+++ b/C/tracer.c
@@ -166,7 +166,7 @@ low_level_trace(yap_low_level_port port, PredEntry *pred, CELL *args)
   }
   switch (port) {
   case enter_pred:
-    mname = RepAtom(AtomOfTerm(Yap_Module_Name((CODEADDR)pred)))->StrOfAE;
+    mname = RepAtom(AtomOfTerm(Yap_Module_Name(pred)))->StrOfAE;
     arity = pred->ArityOfPE;
     if (arity == 0)
       s = RepAtom((Atom)pred->FunctorOfPred)->StrOfAE;
@@ -189,7 +189,7 @@ low_level_trace(yap_low_level_port port, PredEntry *pred, CELL *args)
     if (pred == NULL) {
       send_tracer_message("RETRY TABLE: ", NULL, 0, NULL, args);
     } else {
-      mname = RepAtom(AtomOfTerm(Yap_Module_Name((CODEADDR)pred)))->StrOfAE;
+      mname = RepAtom(AtomOfTerm(Yap_Module_Name(pred)))->StrOfAE;
       arity = pred->ArityOfPE;
       if (arity == 0)
 	s = RepAtom((Atom)pred->FunctorOfPred)->StrOfAE;
@@ -206,7 +206,7 @@ low_level_trace(yap_low_level_port port, PredEntry *pred, CELL *args)
     if (pred == NULL) {
       send_tracer_message("RETRY TABLE: ", NULL, 0, NULL, args);
     } else {
-      mname = RepAtom(AtomOfTerm(Yap_Module_Name((CODEADDR)pred)))->StrOfAE;
+      mname = RepAtom(AtomOfTerm(Yap_Module_Name(pred)))->StrOfAE;
       arity = pred->ArityOfPE;
       if (arity == 0)
 	s = RepAtom((Atom)pred->FunctorOfPred)->StrOfAE;
@@ -220,9 +220,9 @@ low_level_trace(yap_low_level_port port, PredEntry *pred, CELL *args)
   case retry_pred:
     send_tracer_message("FAIL ", NULL, 0, NULL, args);
     if (pred != NULL) {
-      mname = RepAtom(AtomOfTerm(Yap_Module_Name((CODEADDR)pred)))->StrOfAE;
+      mname = RepAtom(AtomOfTerm(Yap_Module_Name(pred)))->StrOfAE;
       arity = pred->ArityOfPE;
-      if (pred->ModuleOfPred == 2) {
+      if (pred->ModuleOfPred == IDB_MODULE) {
 	s = "recorded";
 	arity = 3;
       } else if (arity == 0) {
diff --git a/H/Heap.h b/H/Heap.h
index 481fef1f3..1b4f8a968 100644
--- a/H/Heap.h
+++ b/H/Heap.h
@@ -10,7 +10,7 @@
 * File:		Heap.h         						 *
 * mods:									 *
 * comments:	Heap Init Structure					 *
-* version:      $Id: Heap.h,v 1.56 2004-02-11 13:59:52 vsc Exp $	 *
+* version:      $Id: Heap.h,v 1.57 2004-02-12 12:37:11 vsc Exp $	 *
 *************************************************************************/
 
 /* information that can be stored in Code Space */
@@ -67,7 +67,7 @@ typedef struct thandle {
   UInt ssize;
   UInt tsize;
   Term tdetach;
-  SMALLUNSGN cmod;
+  Term  cmod;
   struct DB_TERM *tgoal;
   int id;
   int ret;
@@ -326,7 +326,12 @@ typedef struct various_codes {
     term_dollar_u,
 #endif
     term_prolog,
-    term_refound_var;
+    term_refound_var,
+    user_module,
+    idb_module,
+    attributes_module,
+    charsio_module,
+    terms_module;
   void *last_wtime;
   struct pred_entry *pred_goal_expansion;
   struct pred_entry *pred_meta_call;
@@ -572,6 +577,12 @@ struct various_codes *heap_regs;
 #define  TermDollarU              heap_regs->term_dollar_u
 #define  TermProlog               heap_regs->term_prolog
 #define  TermReFoundVar           heap_regs->term_refound_var
+#define  PROLOG_MODULE            0
+#define  USER_MODULE              heap_regs->user_module
+#define  IDB_MODULE               heap_regs->idb_module
+#define  ATTRIBUTES_MODULE        heap_regs->attributes_module
+#define  CHARSIO_MODULE           heap_regs->charsio_module
+#define  TERMS_MODULE             heap_regs->terms_module
 #define  PredGoalExpansion        heap_regs->pred_goal_expansion
 #define  PredMetaCall             heap_regs->pred_meta_call
 #define  PredDollarCatch          heap_regs->pred_dollar_catch
@@ -716,13 +727,13 @@ Yap_PreAllocCodeSpace(void)
 
 #if THREADS
 Prop STD_PROTO(Yap_NewThreadPred, (PredEntry *));
-Prop STD_PROTO(Yap_NewPredPropByFunctor, (Functor, SMALLUNSGN));
+Prop STD_PROTO(Yap_NewPredPropByFunctor, (Functor, Term));
 
 EXTERN inline PredEntry *
 Yap_GetThreadPred(PredEntry *ap)
 {
   Functor f = ap->FunctorOfPred;
-  SMALLUNSGN mod = ap->ModuleOfPred;
+  Term  mod = ap->ModuleOfPred;
   Prop p0 = AbsPredProp(heap_regs->thread_handle[worker_id].local_preds);
 
   while(p0) {
diff --git a/H/Regs.h b/H/Regs.h
index fb4791422..6259d3a13 100644
--- a/H/Regs.h
+++ b/H/Regs.h
@@ -10,7 +10,7 @@
 * File:		Regs.h							 *
 * mods:									 *
 * comments:	YAP abstract machine registers				 *
-* version:      $Id: Regs.h,v 1.25 2004-02-11 13:33:19 vsc Exp $	 *
+* version:      $Id: Regs.h,v 1.26 2004-02-12 12:37:11 vsc Exp $	 *
 *************************************************************************/
 
 
@@ -100,7 +100,7 @@ typedef struct
     Term   TermNil_;		/* 20                                         */
 #endif
 #endif
-    SMALLUNSGN  CurrentModule_;
+    Term  CurrentModule_;
 #if defined(SBA) || defined(TABLING)
     CELL *H_FZ_;
     choiceptr B_FZ_;
diff --git a/H/Yapproto.h b/H/Yapproto.h
index daebd1472..7cf404c51 100644
--- a/H/Yapproto.h
+++ b/H/Yapproto.h
@@ -10,7 +10,7 @@
 * File:		Yap.proto						 *
 * mods:									 *
 * comments:	Function declarations for YAP				 *
-* version:      $Id: Yapproto.h,v 1.45 2004-02-11 01:20:56 vsc Exp $	 *
+* version:      $Id: Yapproto.h,v 1.46 2004-02-12 12:37:12 vsc Exp $	 *
 *************************************************************************/
 
 /* prototype file for Yap */
@@ -29,10 +29,10 @@ Term	STD_PROTO(Yap_GetValue,(Atom));
 Atom	STD_PROTO(Yap_LookupAtom,(char *));
 Atom	STD_PROTO(Yap_FullLookupAtom,(char *));
 void	STD_PROTO(Yap_LookupAtomWithAddress,(char *,AtomEntry *));
-Prop	STD_PROTO(Yap_NewPredPropByFunctor,(struct FunctorEntryStruct *, SMALLUNSGN));
-Prop	STD_PROTO(Yap_NewPredPropByAtom,(struct AtomEntryStruct *, SMALLUNSGN));
-Prop	STD_PROTO(Yap_PredPropByFunctorNonThreadLocal,(struct FunctorEntryStruct *, SMALLUNSGN));
-Prop	STD_PROTO(Yap_PredPropByAtomNonThreadLocal,(struct AtomEntryStruct *, SMALLUNSGN));
+Prop	STD_PROTO(Yap_NewPredPropByFunctor,(struct FunctorEntryStruct *, Term));
+Prop	STD_PROTO(Yap_NewPredPropByAtom,(struct AtomEntryStruct *, Term));
+Prop	STD_PROTO(Yap_PredPropByFunctorNonThreadLocal,(struct FunctorEntryStruct *, Term));
+Prop	STD_PROTO(Yap_PredPropByAtomNonThreadLocal,(struct AtomEntryStruct *, Term));
 Functor	STD_PROTO(Yap_UnlockedMkFunctor,(AtomEntry *,unsigned int));
 Functor	STD_PROTO(Yap_MkFunctor,(Atom,unsigned int));
 void	STD_PROTO(Yap_MkFunctorWithAddress,(Atom,unsigned int,FunctorEntry *));
@@ -55,11 +55,11 @@ Term	STD_PROTO(MkSFTerm,(Functor,int,Term *,Term));
 CELL	STD_PROTO(*ArgsOfSFTerm,(Term));
 #endif
 
-Prop	STD_PROTO(Yap_GetPredPropByAtom,(Atom, SMALLUNSGN));
-Prop	STD_PROTO(Yap_GetPredPropByFunc,(Functor, SMALLUNSGN));
-Prop	STD_PROTO(Yap_GetPredPropByAtomInThisModule,(Atom, SMALLUNSGN));
-Prop	STD_PROTO(Yap_GetPredPropByFuncInThisModule,(Functor, SMALLUNSGN));
-Prop	STD_PROTO(Yap_GetPredPropHavingLock,(Atom,unsigned int,SMALLUNSGN));
+Prop	STD_PROTO(Yap_GetPredPropByAtom,(Atom, Term));
+Prop	STD_PROTO(Yap_GetPredPropByFunc,(Functor, Term));
+Prop	STD_PROTO(Yap_GetPredPropByAtomInThisModule,(Atom, Term));
+Prop	STD_PROTO(Yap_GetPredPropByFuncInThisModule,(Functor, Term));
+Prop	STD_PROTO(Yap_GetPredPropHavingLock,(Atom,unsigned int, Term));
 Prop	STD_PROTO(Yap_GetExpProp,(Atom,unsigned int));
 Prop	STD_PROTO(Yap_GetExpPropHavingLock,(AtomEntry *,unsigned int));
 
@@ -107,7 +107,7 @@ Int    STD_PROTO(YAP_Execute,(struct pred_entry *, CPredicate));
 /* cdmgr.c */
 Term	STD_PROTO(Yap_all_calls,(void));
 Atom	STD_PROTO(Yap_ConsultingFile,(void));
-Int	STD_PROTO(Yap_PredForCode,(yamop *, Atom *, UInt *, SMALLUNSGN *));
+Int	STD_PROTO(Yap_PredForCode,(yamop *, Atom *, UInt *, Term *));
 void	STD_PROTO(Yap_InitCdMgr,(void));
 #if     EMACS
 int     STD_PROTO(where_new_clause, (Prop, int));
@@ -148,11 +148,11 @@ yamop  *STD_PROTO(Yap_Error,(yap_error_number,Term,char *msg, ...));
 void	STD_PROTO(Yap_InitEval,(void));
 
 /* exec.c */
-Term	STD_PROTO(Yap_ExecuteCallMetaCall,(SMALLUNSGN mod));
+Term	STD_PROTO(Yap_ExecuteCallMetaCall,(Term));
 void	STD_PROTO(Yap_InitExecFs,(void));
 Int	STD_PROTO(Yap_JumpToEnv,(Term));
 int	STD_PROTO(Yap_RunTopGoal,(Term));
-Int	STD_PROTO(Yap_execute_goal,(Term, int, SMALLUNSGN));
+Int	STD_PROTO(Yap_execute_goal,(Term, int, Term));
 int	STD_PROTO(Yap_exec_absmi,(int));
 void	STD_PROTO(Yap_trust_last,(void));
 
@@ -214,8 +214,9 @@ Term	STD_PROTO(Yap_ReadTimedVar,(Term));
 Term    STD_PROTO(Yap_UpdateTimedVar,(Term, Term));
 
 /* modules.c */
-SMALLUNSGN	STD_PROTO(Yap_LookupModule,(Term));
-Term    STD_PROTO(Yap_Module_Name, (CODEADDR));
+Term    STD_PROTO(Yap_Module_Name, (struct pred_entry *));
+struct pred_entry *STD_PROTO(Yap_ModulePred, (Term));
+void    STD_PROTO(Yap_NewModulePred, (Term, struct pred_entry *));
 void    STD_PROTO(Yap_InitModules, (void));
 void    STD_PROTO(Yap_InitModulesC, (void));
 
diff --git a/H/amidefs.h b/H/amidefs.h
index 28017a6ca..d31d96258 100644
--- a/H/amidefs.h
+++ b/H/amidefs.h
@@ -386,7 +386,7 @@ typedef struct yami {
 	 union {
 	   struct yami *l;
 	   struct pred_entry  *p;
-	   SMALLUNSGN  m_num;
+	   Term  mod;
 	 } sla_u;
          struct pred_entry  *p0;
 	 CELL next;
diff --git a/H/clause.h b/H/clause.h
index 759118f2f..53c9ac558 100644
--- a/H/clause.h
+++ b/H/clause.h
@@ -169,11 +169,11 @@ void    STD_PROTO(Yap_InitComma,(void));
 /* cdmgr.c */
 void	STD_PROTO(Yap_RemoveLogUpdIndex,(LogUpdIndex *));
 void	STD_PROTO(Yap_IPred,(PredEntry *));
-void	STD_PROTO(Yap_addclause,(Term,yamop *,int,int));
+void	STD_PROTO(Yap_addclause,(Term,yamop *,int,Term));
 void	STD_PROTO(Yap_add_logupd_clause,(PredEntry *,LogUpdClause *,int));
 void	STD_PROTO(Yap_kill_iblock,(ClauseUnion *,ClauseUnion *,PredEntry *));
 void	STD_PROTO(Yap_cleanup_dangling_indices,(yamop *,yamop *,yamop *,yamop *));
-void	STD_PROTO(Yap_EraseStaticClause,(StaticClause *, SMALLUNSGN));
+void	STD_PROTO(Yap_EraseStaticClause,(StaticClause *, Term));
 ClauseUnion *STD_PROTO(Yap_find_owner_index,(yamop *, PredEntry *));
 
 /* dbase.c */
diff --git a/H/compile.h b/H/compile.h
index ab2765ef6..026d37935 100644
--- a/H/compile.h
+++ b/H/compile.h
@@ -256,7 +256,7 @@ void	STD_PROTO(Yap_emit_3ops,(compiler_vm_op,CELL,CELL,CELL, struct intermediate
 void	STD_PROTO(Yap_emit_4ops,(compiler_vm_op,CELL,CELL,CELL,CELL, struct intermediates *));
 CELL   *STD_PROTO(Yap_emit_extra_size,(compiler_vm_op,CELL,int, struct intermediates *));
 char   *STD_PROTO(Yap_AllocCMem,(int, struct intermediates *));
-int	STD_PROTO(Yap_is_a_test_pred,(Term, SMALLUNSGN));
+int	STD_PROTO(Yap_is_a_test_pred,(Term, Term));
 void    STD_PROTO(Yap_bip_name,(Int, char *));
 #ifdef DEBUG
 void	STD_PROTO(Yap_ShowCode,(struct intermediates *));
diff --git a/H/rheap.h b/H/rheap.h
index a097a53cf..7fdfbc426 100644
--- a/H/rheap.h
+++ b/H/rheap.h
@@ -305,6 +305,11 @@ restore_codes(void)
 #endif
   heap_regs->term_prolog = AtomTermAdjust(heap_regs->term_prolog);
   heap_regs->term_refound_var = AtomTermAdjust(heap_regs->term_refound_var);
+  heap_regs->user_module = AtomTermAdjust(heap_regs->user_module);
+  heap_regs->idb_module = AtomTermAdjust(heap_regs->idb_module);
+  heap_regs->attributes_module = AtomTermAdjust(heap_regs->attributes_module);
+  heap_regs->charsio_module = AtomTermAdjust(heap_regs->charsio_module);
+  heap_regs->terms_module = AtomTermAdjust(heap_regs->terms_module);
   if (heap_regs->dyn_array_list != NULL) {
     heap_regs->dyn_array_list =
       (struct array_entry *)AddrAdjust((ADDR)heap_regs->dyn_array_list);
@@ -1516,8 +1521,8 @@ CleanCode(PredEntry *pp)
     pp->FunctorOfPred = FuncAdjust(pp->FunctorOfPred);
   else
     pp->FunctorOfPred = (Functor)AtomAdjust((Atom)(pp->FunctorOfPred));
-  if (pp->ModuleOfPred != 2) {
-    if (pp->src.OwnerFile && pp->ModuleOfPred != 2)
+  if (pp->ModuleOfPred != IDB_MODULE) {
+    if (pp->src.OwnerFile && pp->ModuleOfPred != IDB_MODULE)
       pp->src.OwnerFile = AtomAdjust(pp->src.OwnerFile);
   }
   if (!(pp->PredFlags & NumberDBPredFlag)) {
diff --git a/OPTYap/opt.preds.c b/OPTYap/opt.preds.c
index 881b4ff1d..1de8c9a8e 100644
--- a/OPTYap/opt.preds.c
+++ b/OPTYap/opt.preds.c
@@ -151,15 +151,12 @@ int start_yapor(void) {
 
 static
 int p_sequential(void) {
-  Term t, tmod;
-  SMALLUNSGN mod;
+  Term t, mod;
   PredEntry *pe;
 
-  tmod = Deref(ARG2);
-  if (IsVarTerm(tmod) || !IsAtomTerm(tmod)) {
+  mod = Deref(ARG2);
+  if (IsVarTerm(mod) || !IsAtomTerm(mod)) {
     return(FALSE);
-  } else {
-    mod = Yap_LookupModule(tmod);
   }
   t = Deref(ARG1);
   if (IsAtomTerm(t)) {
@@ -447,17 +444,14 @@ void answer_to_stdout(char *answer) {
 #ifdef TABLING
 static
 int p_table(void) {
-  Term t, tmod;
-  SMALLUNSGN mod;
+  Term t, mod;
   PredEntry *pe;
   tab_ent_ptr te;
   sg_node_ptr sg_node;
 
   tmod = Deref(ARG2);
-  if (IsVarTerm(tmod) || !IsAtomTerm(tmod)) {
+  if (IsVarTerm(mod) || !IsAtomTerm(mod)) {
     return (FALSE);
-  } else {
-    mod = Yap_LookupModule(tmod);
   }
   t = Deref(ARG1);
   if (IsAtomTerm(t)) {
@@ -479,18 +473,15 @@ int p_table(void) {
 
 static
 int p_abolish_trie(void) {
-  Term t, tmod;
-  SMALLUNSGN mod;
+  Term t, mod;
   tab_ent_ptr tab_ent;
   sg_hash_ptr hash;
   sg_node_ptr sg_node;
   UInt arity;
 
-  tmod = Deref(ARG2);
-   if (IsVarTerm(tmod) || !IsAtomTerm(tmod)) {
+  mod = Deref(ARG2);
+   if (IsVarTerm(mod) || !IsAtomTerm(mod)) {
     return (FALSE);
-  } else {
-    mod = Yap_LookupModule(tmod);
   } 
   t = Deref(ARG1);
   if (IsAtomTerm(t)) {
@@ -518,17 +509,14 @@ int p_abolish_trie(void) {
 
 static
 int p_show_trie(void) {
-  Term t1, t2, tmod;
-  SMALLUNSGN mod;
+  Term t1, t2, mod;
   PredEntry *pe;
   Atom at;
   UInt arity;
 
-  tmod = Deref(ARG2);
-   if (IsVarTerm(tmod) || !IsAtomTerm(tmod)) {
+  mod = Deref(ARG2);
+   if (IsVarTerm(mod) || !IsAtomTerm(mod)) {
     return (FALSE);
-  } else {
-    mod = Yap_LookupModule(tmod);
   } 
   t1 = Deref(ARG1);
   if (IsAtomTerm(t1)) {
@@ -564,17 +552,14 @@ int p_show_trie(void) {
 
 static
 int p_resume_trie(void) {
-  Term t, tmod;
-  SMALLUNSGN mod;
+  Term t, mod;
   PredEntry *pe;
   Atom at;
   int arity;
 
-  tmod = Deref(ARG2);
-  if (IsVarTerm(tmod) || !IsAtomTerm(tmod)) {
+  mod = Deref(ARG2);
+  if (IsVarTerm(mod) || !IsAtomTerm(mod)) {
     return (FALSE);
-  } else {
-    mod = Yap_LookupModule(tmod);
   } 
   t = Deref(ARG1);
   if (IsAtomTerm(t)) {
diff --git a/include/YapInterface.h b/include/YapInterface.h
index bde099434..e506aff31 100644
--- a/include/YapInterface.h
+++ b/include/YapInterface.h
@@ -308,7 +308,7 @@ extern X_API void PROTO(YAP_RecoverSlots,(int));
 extern X_API void PROTO(YAP_Throw,(YAP_Term));
 
 /*  int  YAP_LookupModule()  */
-extern X_API int  PROTO(YAP_LookupModule,(YAP_Term));
+#define YAP_LookupModule(T)  (T)
 
 /*  int  YAP_ModuleName()  */
 extern X_API YAP_Term  PROTO(YAP_ModuleName,(int));
diff --git a/m4/Yatom.h.m4 b/m4/Yatom.h.m4
index 9f35a7139..4ce7390f9 100644
--- a/m4/Yatom.h.m4
+++ b/m4/Yatom.h.m4
@@ -64,7 +64,7 @@ Inline(IsFunctorProperty, PropFlags, int, flags, (flags == FunctorProperty) )
 typedef struct {
     Prop   	NextOfPE;	/* used	to chain properties		*/
     PropFlags  	KindOfPE;	/* kind	of property			*/
-    SMALLUNSGN  IndexOfMod;     /* indec in module table		*/
+    SMALLUNSGN  IndexOfMod;     /* index in module table		*/
 } ModEntry;
 
 #if USE_OFFSETS_IN_PROPS
@@ -237,7 +237,7 @@ typedef	struct pred_entry {
 #ifdef TABLING
   tab_ent_ptr   TableOfPred;
 #endif /* TABLING */
-  SMALLUNSGN	ModuleOfPred;	/* module for this definition		*/
+  Term 	ModuleOfPred;	/* module for this definition		*/
   /* This must be at an odd number of cells, otherwise it
      will not be aligned on RISC machines */
   profile_data  StatisticsForPred; /* enable profiling for predicate  */
@@ -342,7 +342,7 @@ typedef	struct struct_dbentry {
 #endif
   DBRef	First;		/* first DBase entry			*/
   DBRef	Last;		/* last DBase entry			*/
-  SMALLUNSGN	ModuleOfDB;	/* module for this definition		*/
+  Term 	ModuleOfDB;	/* module for this definition		*/
   DBRef         F0,L0;		/* everyone                          */
 } DBEntry;
 typedef DBEntry *DBProp;
@@ -358,7 +358,7 @@ typedef	struct {
 #endif 
   DBRef	First;		/* first DBase entry			*/
   DBRef	Last;		/* last DBase entry			*/
-  SMALLUNSGN	ModuleOfDB;	/* module for this definition		*/
+  Term	ModuleOfDB;	/* module for this definition		*/
   Int         NOfEntries;	/* age counter                          */
   DBRef       Index;		/* age counter                          */
 } LogUpdDBEntry;
@@ -400,7 +400,7 @@ typedef	struct {
 #if defined(YAPOR) || defined(THREADS)
   rwlock_t BBRWLock;            /* a read-write lock to protect the entry */
 #endif
-  SMALLUNSGN	ModuleOfBB;   /* module for this definition		*/
+  Term	ModuleOfBB;   /* module for this definition		*/
 } BlackBoardEntry;
 typedef BlackBoardEntry *BBProp;
 
@@ -509,7 +509,7 @@ EXTERN inline PredEntry *STD_PROTO(Yap_GetThreadPred, (PredEntry *));
 #endif
 
 EXTERN inline Prop
-PredPropByFunc(Functor f, SMALLUNSGN cur_mod)
+PredPropByFunc(Functor f, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
@@ -537,7 +537,7 @@ PredPropByFunc(Functor f, SMALLUNSGN cur_mod)
 }
 
 EXTERN inline Prop
-PredPropByAtom(Atom at, SMALLUNSGN cur_mod)
+PredPropByAtom(Atom at, Term cur_mod)
 /* get predicate entry for ap/arity; create it if neccessary.              */
 {
   Prop p0;
diff --git a/pl/arith.yap b/pl/arith.yap
index 15a150059..05eb75d20 100644
--- a/pl/arith.yap
+++ b/pl/arith.yap
@@ -85,14 +85,12 @@ do_not_compile_expressions :- set_value('$c_arith',[]).
 
 '$do_c_built_metacall'(G1, Mod, call(Mod:G1)) :- 
 	var(G1), var(Mod), !.
-'$do_c_built_metacall'(G1, Mod, '$execute_in_mod'(G1,MNum)) :- 
-	var(G1), atom(Mod), !,
-	'$module_number'(Mod,MNum).
+'$do_c_built_metacall'(G1, Mod, '$execute_in_mod'(G1,Mod)) :- 
+	var(G1), atom(Mod), !.
 '$do_c_built_metacall'(Mod:G1, _, call(Mod:G1)) :-  !,
 	'$do_c_built_metacall'(G1, Mod, OUT).
-'$do_c_built_metacall'(G1, Mod, '$execute_in_mod'(G1,MNum)) :-
-	atom(Mod), !,
-	'$module_number'(Mod,MNum).
+'$do_c_built_metacall'(G1, Mod, '$execute_in_mod'(G1,Mod)) :-
+	atom(Mod), !.
 '$do_c_built_metacall'(G1, Mod, call(Mod:G1)).
 
 
diff --git a/pl/corout.yap b/pl/corout.yap
index 776f619ce..0ba8f661d 100644
--- a/pl/corout.yap
+++ b/pl/corout.yap
@@ -83,7 +83,6 @@
         '$undefp'([Module1|Continuation]).
 '$execute_continuation'(Continuation, Mod) :-
          % do not do meta-expansion nor any fancy stuff.
-'$module_number'(Mod,_),
 	'$execute0'(Continuation, Mod).
 
 
diff --git a/pl/init.yap b/pl/init.yap
index 8748c1154..157044919 100644
--- a/pl/init.yap
+++ b/pl/init.yap
@@ -134,4 +134,3 @@ library_directory(D) :-
 	getenv('YAPSHAREDIR', D).
 
 :- get_value(system_library_directory,D), assert(library_directory(D)).
-