diff --git a/C/alloc.c b/C/alloc.c
index d2d7e8814..699f80523 100644
--- a/C/alloc.c
+++ b/C/alloc.c
@@ -61,14 +61,57 @@ static char SccsId[] = "%W% %G%";
 /************************************************************************/
 /* Yap workspace management                                             */
 
-#if USE_DL_MALLOC
-#define malloc Yap_dlmalloc
-#define free Yap_dlfree
-#define realloc Yap_dlrealloc
+#if USE_SYSTEM_MALLOC
+#define my_malloc(sz) malloc(sz)
+#define my_realloc(ptr, sz, safe) realloc(ptr, sz)
+#define my_free(ptr) free(ptr)
 #else
-void Yap_add_memory_hole(ADDR Start, ADDR End)
+#define my_malloc(sz) Yap_dlmalloc(sz)
+#define my_free(sz) Yap_dlfree(sz)
+
+static char * my_realloc(char *ptr, UInt sz, UInt osz, int safe)
 {
-  Yap_HoleSize += Start-End;
+  char *nptr;
+
+ restart:
+  /* simple case */
+  if (ptr < Yap_HeapBase || ptr > HeapTop) {
+    /* we have enough room */
+    nptr = Yap_dlmalloc(sz);
+    if (nptr) {
+      memmove(nptr, ptr, osz);
+      free(ptr);
+    }
+  } else {
+    nptr = Yap_dlrealloc(ptr, sz);
+  }
+  if (nptr) {
+    return nptr;
+  }
+  /* we do not have enough room */
+  if (safe) {
+    if (Yap_growheap(FALSE, sz, NULL)) {
+      /* now, we have room */
+      goto restart;
+    }
+  }
+  /* no room in Heap, gosh */
+  if (ptr < Yap_HeapBase || ptr > HeapTop) {
+    /* try expanding outside the heap */
+    nptr = realloc(ptr, sz);
+    if (nptr) {
+      memmove(nptr, ptr, osz);
+    }
+  } else {
+    /* try calling the outside world for help */
+    nptr = malloc(sz);
+    if (!nptr)
+      return NULL;
+    memmove(nptr, ptr, osz);
+    Yap_dlfree(ptr);
+  }
+  /* did we suceed? at this point we could not care less */
+  return nptr;
 }
 #endif
 
@@ -98,7 +141,7 @@ call_malloc(unsigned long int size)
   tmalloc += size;
 #endif
   Yap_PrologMode |= MallocMode;
-  out = (char *) malloc(size);
+  out = (char *) my_malloc(size);
   Yap_PrologMode &= ~MallocMode;
   return out;
 }
@@ -119,7 +162,7 @@ Yap_FreeCodeSpace(char *p)
     minfo('F');
   frees++;
 #endif
-  free (p);
+  my_free (p);
   Yap_PrologMode &= ~MallocMode;
 }
 
@@ -138,7 +181,7 @@ Yap_FreeAtomSpace(char *p)
     minfo('F');
   frees++;
 #endif
-  free (p);
+  my_free (p);
   Yap_PrologMode &= ~MallocMode;
 }
 
@@ -153,7 +196,7 @@ Yap_InitPreAllocCodeSpace(void)
   UInt sz = ScratchPad.msz;
   if (ScratchPad.ptr == NULL) {
     Yap_PrologMode |= MallocMode;
-    while (!(ptr = malloc(sz))) {
+    while (!(ptr = my_malloc(sz))) {
       Yap_PrologMode &= ~MallocMode;
       if (!Yap_growheap(FALSE, Yap_Error_Size, NULL)) {
 	Yap_Error(OUT_OF_HEAP_ERROR, TermNil, Yap_ErrorMessage);
@@ -166,12 +209,13 @@ Yap_InitPreAllocCodeSpace(void)
   } else {
     ptr = ScratchPad.ptr;
   }
-  AuxSp = (CELL *)(AuxTop = (ADDR)(ptr+ScratchPad.sz));
+  AuxBase = (ADDR)(ptr);
+  AuxSp = (CELL *)(AuxTop = AuxBase+ScratchPad.sz);
   return ptr;
 }
 
 ADDR
-Yap_ExpandPreAllocCodeSpace(UInt sz0, void *cip)
+Yap_ExpandPreAllocCodeSpace(UInt sz0, void *cip, int safe)
 {
   char *ptr;
   UInt sz = ScratchPad.msz;
@@ -189,20 +233,14 @@ Yap_ExpandPreAllocCodeSpace(UInt sz0, void *cip)
   reallocs++;
 #endif
   Yap_PrologMode |= MallocMode;
-  while (!(ptr = realloc(ScratchPad.ptr, sz))) {
+  if (!(ptr = my_realloc(ScratchPad.ptr, sz, ScratchPad.sz, safe))) {
     Yap_PrologMode &= ~MallocMode;
-#if USE_DL_MALLOC
-    if (!Yap_growheap((cip!=NULL), sz, cip)) {
-      return NULL;
-    }
-#else
     return NULL;
-#endif
-    Yap_PrologMode |= MallocMode;
   }
   Yap_PrologMode &= ~MallocMode;
   ScratchPad.sz = ScratchPad.msz = sz;
   ScratchPad.ptr = ptr;
+  AuxBase = ptr;
   AuxSp = (CELL *)(AuxTop = ptr+sz);
   return ptr;
 }
@@ -1420,6 +1458,14 @@ Yap_InitExStacks(int Trail, int Stack)
 #define MAP_FIXED 1
 #endif
 
+#if !USE_DL_MALLOC
+/* dead code */
+void Yap_add_memory_hole(ADDR Start, ADDR End)
+{
+  Yap_HoleSize += Start-End;
+}
+#endif
+
 int
 Yap_ExtendWorkSpace(Int s)
 {
diff --git a/C/amasm.c b/C/amasm.c
index b1a469679..60ffdf83c 100644
--- a/C/amasm.c
+++ b/C/amasm.c
@@ -3780,7 +3780,7 @@ fetch_clause_space(Term* tp, UInt size, struct intermediates *cip, UInt *osizep)
       break;
     case OUT_OF_AUXSPACE_ERROR:
       ARG1 = *tp;
-      if (!Yap_ExpandPreAllocCodeSpace(Yap_Error_Size, (void *)cip)) {
+      if (!Yap_ExpandPreAllocCodeSpace(Yap_Error_Size, (void *)cip, TRUE)) {
 	return NULL;
       }
       Yap_Error_TYPE = YAP_NO_ERROR;
diff --git a/C/compiler.c b/C/compiler.c
index 4699e1e95..cdf548b27 100644
--- a/C/compiler.c
+++ b/C/compiler.c
@@ -3347,7 +3347,7 @@ Yap_cclause(volatile Term inp_clause, int NOfArgs, Term mod, volatile Term src)
       YAPLeaveCriticalSection();
       ARG1 = inp_clause;
       ARG3 = src;
-      if (!Yap_ExpandPreAllocCodeSpace(Yap_Error_Size, NULL)) {
+      if (!Yap_ExpandPreAllocCodeSpace(Yap_Error_Size, NULL, TRUE)) {
 	Yap_Error_TYPE = OUT_OF_AUXSPACE_ERROR;
 	Yap_Error_Term = inp_clause;
       }
diff --git a/C/corout.c b/C/corout.c
index fd8d200d7..f9d7a605d 100644
--- a/C/corout.c
+++ b/C/corout.c
@@ -503,7 +503,7 @@ non_ground(Term t, Term *Var)
       if (out >= 0)
 	return out;
     }
-    if (!Yap_ExpandPreAllocCodeSpace(0, NULL)) {
+    if (!Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE)) {
       Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "overflow in ground");
       return FALSE;
     }      
diff --git a/C/dbase.c b/C/dbase.c
index c58eec95f..44ddfa0b4 100644
--- a/C/dbase.c
+++ b/C/dbase.c
@@ -279,7 +279,7 @@ recover_from_record_error(int nargs)
     }
     goto recover_record;
   case OUT_OF_AUXSPACE_ERROR:
-    if (!Yap_ExpandPreAllocCodeSpace(Yap_Error_Size, NULL)) {
+    if (!Yap_ExpandPreAllocCodeSpace(Yap_Error_Size, NULL, TRUE)) {
       Yap_Error(OUT_OF_AUXSPACE_ERROR, Yap_Error_Term, Yap_ErrorMessage);
       return FALSE;
     }
diff --git a/C/exec.c b/C/exec.c
index b795a316c..7273dde00 100644
--- a/C/exec.c
+++ b/C/exec.c
@@ -1652,7 +1652,7 @@ Yap_InitYaamRegs(void)
   PREG_ADDR = NULL;
 #endif
   Yap_AllocateDefaultArena(128*1024, 2);
-  Yap_PreAllocCodeSpace();
+  Yap_InitPreAllocCodeSpace();
 #ifdef CUT_C
   cut_c_initialize();
 #endif
diff --git a/C/globals.c b/C/globals.c
index 625c66cf9..3255a80db 100644
--- a/C/globals.c
+++ b/C/globals.c
@@ -889,7 +889,7 @@ CopyTermToArena(Term t, Term arena, int share, UInt arity, Term *newarena, Term
       }
       break;
     default: /* temporary space overflow */
-      if (!Yap_ExpandPreAllocCodeSpace(0,NULL)) {
+      if (!Yap_ExpandPreAllocCodeSpace(0,NULL,TRUE)) {
 	Yap_Error(OUT_OF_AUXSPACE_ERROR, TermNil, Yap_ErrorMessage);
 	return 0L;
       }
diff --git a/C/gprof.c b/C/gprof.c
index e16e788a3..44819276b 100644
--- a/C/gprof.c
+++ b/C/gprof.c
@@ -732,7 +732,7 @@ search_pc_pred(yamop *pc_ptr,clauseentry *beg, clauseentry *end) {
 }
 
 extern void Yap_InitAbsmi(void);
-extern int rational_tree_loop(CELL *pt0, CELL *pt0_end, CELL **to_visit0);
+extern int Yap_rational_tree_loop(CELL *pt0, CELL *pt0_end, CELL **to_visit0, CELL **to_visit_max);
 
 static Int profend(void); 
 
@@ -788,7 +788,7 @@ showprofres(UInt type) {
         if ((unsigned long)oldpc & GCMode) { InGC++; continue; }
         if ((unsigned long)oldpc & (ErrorHandlingMode | InErrorMode)) { InError++; continue; }
       }
-      if (oldpc>(void *) rational_tree_loop && oldpc<(void *) Yap_InitAbsmi) { InUnify++; continue; }
+      if (oldpc>(void *) Yap_rational_tree_loop && oldpc<(void *) Yap_InitAbsmi) { InUnify++; continue; }
       y=(yamop *) ((long) pc_ptr-20);
       if (y->opc==Yap_opcode(_call_cpred) || y->opc==Yap_opcode(_call_usercpred)) {
              InCCall++;  /* I Was in a C Call */
diff --git a/C/grow.c b/C/grow.c
index 4fc92953a..1933d3a19 100644
--- a/C/grow.c
+++ b/C/grow.c
@@ -1606,41 +1606,39 @@ Yap_growtrail_in_parser(tr_fr_ptr *old_trp, TokEntry **tksp, VarEntry **vep)
 CELL **
 Yap_shift_visit(CELL **to_visit, CELL ***to_visit_maxp)
 {
-#if USE_SYSTEM_MALLOC
   CELL **to_visit_max = *to_visit_maxp;
-  Int sz1 = (CELL)to_visit-(CELL)to_visit_max;
-  Int sz0 = AuxTop - (ADDR)to_visit_max, sz, dsz;
-  char *newb = Yap_ExpandPreAllocCodeSpace(0, NULL);
+  /* relative position of top of stack */
+  Int off = (ADDR)to_visit-AuxBase;
+  /* how much space the top stack was using */
+  Int sz = AuxTop - (ADDR)to_visit_max;
+  /* how much space the bottom stack was using */
+  Int szlow = (ADDR)to_visit_max-AuxBase;
+  /* original size for AuxSpace */
+  Int totalsz0 = AuxTop - AuxBase; /* totalsz0 == szlow+sz */
+  /* new size for AuxSpace */
+  Int totalsz;
+  /* how much we grow */
+  Int dsz; /* totalsz == szlow+dsz+sz */
+  char *newb = Yap_ExpandPreAllocCodeSpace(0, NULL, FALSE);
 
   if (newb == NULL) {
     Yap_Error(OUT_OF_HEAP_ERROR,TermNil,"cannot allocate temporary space for unification (%p)", to_visit);       
     return to_visit;
   }
   /* check new size */
-  sz = AuxTop-newb;
+  totalsz  = AuxTop-AuxBase;
   /* how much we grew */
-  dsz = sz-sz0;
+  dsz = totalsz-totalsz0;
   if (dsz == 0) {
     Yap_Error(OUT_OF_HEAP_ERROR,TermNil,"cannot allocate temporary space for unification (%p)", to_visit);       
     return to_visit;
   }
   /* copy whole block to end */
-  cpcellsd((CELL *)newb, (CELL *)(newb+dsz), sz0/sizeof(CELL));
+  cpcellsd((CELL *)(newb+(dsz+szlow)), (CELL *)(newb+szlow), sz/sizeof(CELL));
   /* base pointer is block start */
-  *to_visit_maxp = (CELL **)newb;
+  *to_visit_maxp = (CELL **)(newb+szlow);
   /* current top is originall diff + diff size */
-  return (CELL **)((char *)newb+(sz1+dsz));
-#else
-  CELL **old_top = (CELL **)Yap_TrailTop;
-  if (do_growtrail(64 * 1024L, FALSE, FALSE, NULL, NULL, NULL)) {
-    CELL **dest = (CELL **)((char *)to_visit+(Yap_TrailTop-(ADDR)old_top));
-    cpcellsd((CELL *)dest, (CELL *)to_visit, (CELL)((CELL *)old_top-(CELL *)to_visit));
-    return dest;
-  } else {
-    Yap_Error(OUT_OF_TRAIL_ERROR,TermNil,"cannot grow temporary stack for unification (%p)", Yap_TrailTop);    
-    return to_visit;
-  }
-#endif
+  return (CELL **)(newb+(off+dsz));
 }
 
 static Int
diff --git a/C/heapgc.c b/C/heapgc.c
index 6cfeff8cf..548ddc43c 100644
--- a/C/heapgc.c
+++ b/C/heapgc.c
@@ -3772,7 +3772,7 @@ do_gc(Int predarity, CELL *current_env, yamop *nextop)
   while (Yap_bp+alloc_sz > (char *)AuxSp) {
     /* not enough space */
     *--ASP = (CELL)current_env;
-    Yap_bp = (char *)Yap_ExpandPreAllocCodeSpace(alloc_sz, NULL);
+    Yap_bp = (char *)Yap_ExpandPreAllocCodeSpace(alloc_sz, NULL, TRUE);
     if (!Yap_bp)
       return -1;
     current_env = (CELL *)*ASP;
diff --git a/C/iopreds.c b/C/iopreds.c
index 1ebb92394..097734475 100644
--- a/C/iopreds.c
+++ b/C/iopreds.c
@@ -3936,7 +3936,7 @@ static Int
 	  }
 	} else if (Yap_Error_TYPE == OUT_OF_AUXSPACE_ERROR) {
 	  Yap_Error_TYPE = YAP_NO_ERROR;
-	  if (!Yap_ExpandPreAllocCodeSpace(0, NULL)) {
+	  if (!Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE)) {
 	    return FALSE;
 	  }
 	} else if (Yap_Error_TYPE == OUT_OF_HEAP_ERROR) {
diff --git a/C/save.c b/C/save.c
index d363c80b2..8eae21322 100644
--- a/C/save.c
+++ b/C/save.c
@@ -1230,10 +1230,17 @@ RestoreFreeSpace(void)
 #if USE_DL_MALLOC
   Yap_av = (struct malloc_state *)AddrAdjust((ADDR)Yap_av);
   Yap_RestoreDLMalloc();
-  if (AuxSp != NULL)
-    AuxSp = PtoHeapCellAdjust(AuxSp);
-  if (AuxTop != NULL)
-    AuxTop = AddrAdjust(AuxTop);
+  if (AuxSp != NULL) {
+    if (AuxBase < OldHeapBase || AuxBase > OldHeapTop) {
+      AuxSp = NULL;
+      AuxBase = NULL;
+      AuxTop = NULL;
+    } else {
+      AuxSp = PtoHeapCellAdjust(AuxSp);
+      AuxBase = AddrAdjust(AuxBase);
+      AuxTop = AddrAdjust(AuxTop);
+    }
+  }
 #else
   /* restores the list of free space, with its curious structure */
   BlockHeader *bpt, *bsz;
@@ -1765,6 +1772,11 @@ Restore(char *s, char *lib_dir)
   /* reset time */
   Yap_ReInitWallTime();
   Yap_InitSysPath();
+#if USE_DL_MALLOC || USE_SYSTEM_MALLOC
+  if (!AuxSp) {
+    Yap_InitPreAllocCodeSpace();
+  }
+#endif
   CloseRestore();
   if (which_save == 2) {
     Yap_unify(ARG2, MkIntTerm(0));
diff --git a/C/stdpreds.c b/C/stdpreds.c
index 7d473dc76..ced0083d4 100644
--- a/C/stdpreds.c
+++ b/C/stdpreds.c
@@ -1065,7 +1065,7 @@ p_name(void)
 
   /* error handling */
  expand_auxsp:
-  String = Yap_ExpandPreAllocCodeSpace(0,NULL);
+  String = Yap_ExpandPreAllocCodeSpace(0,NULL, TRUE);
   if (String + 1024 > (char *)AuxSp) {
     /* crash in flames */
     Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "allocating temp space in name/2");
@@ -1246,7 +1246,7 @@ p_atom_chars(void)
   }
   /* error handling */
  expand_auxsp:
-  String = Yap_ExpandPreAllocCodeSpace(0,NULL);
+  String = Yap_ExpandPreAllocCodeSpace(0,NULL, TRUE);
   if (String + 1024 > (char *)AuxSp) {
     /* crash in flames */
     Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "allocating temp space in atom_chars/2");
@@ -1407,7 +1407,7 @@ p_atomic_concat(void)
  restart:
   base = ((AtomEntry *)Yap_PreAllocCodeSpace())->StrOfAE;
   while (base+1024 > (char *)AuxSp) {
-    base = Yap_ExpandPreAllocCodeSpace(0,NULL);
+    base = Yap_ExpandPreAllocCodeSpace(0,NULL, TRUE);
     if (base + 1024 > (char *)AuxSp) {
       /* crash in flames */
       Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "allocating temp space in atomic_concat/2");
@@ -1727,7 +1727,7 @@ p_atom_codes(void)
   /* error handling */
  expand_auxsp:
   if (String + 1024 > (char *)AuxSp) { 
-    String = Yap_ExpandPreAllocCodeSpace(0,NULL);
+    String = Yap_ExpandPreAllocCodeSpace(0,NULL, TRUE);
   
     if (String + 1024 > (char *)AuxSp) {
       /* crash in flames */
@@ -1914,7 +1914,7 @@ p_number_chars(void)
  restart_aux:
   String = Yap_PreAllocCodeSpace();
   if (String+1024 > (char *)AuxSp) {
-    String = Yap_ExpandPreAllocCodeSpace(0,NULL);
+    String = Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE);
     if (String + 1024 > (char *)AuxSp) {
       /* crash in flames */
       Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "allocating temp space in number_chars/2");
@@ -1980,7 +1980,7 @@ p_number_chars(void)
       }
       if (s+1024 > (char *)AuxSp) {
 	int offs = (s-String);
-	String = Yap_ExpandPreAllocCodeSpace(0,NULL);
+	String = Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE);
 	if (String + (offs+1024) > (char *)AuxSp) {
 	  /* crash in flames */
 	  Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "allocating temp space in number_chars/2");
@@ -2021,7 +2021,7 @@ p_number_chars(void)
 	char *nString;
 
 	*H++ = t;
-	nString = Yap_ExpandPreAllocCodeSpace(0,NULL);
+	nString = Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE);
 	t = *--H;
 	s = nString+(s-String);
 	String = nString;
@@ -2055,7 +2055,7 @@ p_number_atom(void)
 
   s = String = ((AtomEntry *)Yap_PreAllocCodeSpace())->StrOfAE;
   if (String+1024 > (char *)AuxSp) {
-    s = String = Yap_ExpandPreAllocCodeSpace(0,NULL);
+    s = String = Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE);
     if (String + 1024 > (char *)AuxSp) {
       /* crash in flames */
       Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "allocating temp space in number_atom/2");
@@ -2124,7 +2124,7 @@ p_number_codes(void)
 
   String = Yap_PreAllocCodeSpace();
   if (String+1024 > (char *)AuxSp) {
-    s = String = Yap_ExpandPreAllocCodeSpace(0,NULL);
+    s = String = Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE);
     if (String + 1024 > (char *)AuxSp) {
       /* crash in flames */
       Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "allocating temp space in number_codes/2");
@@ -2186,7 +2186,7 @@ p_number_codes(void)
       char *nString;
 
       *H++ = t;
-      nString = Yap_ExpandPreAllocCodeSpace(0,NULL);
+      nString = Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE);
       t = *--H;
       s = nString+(s-String);
       String = nString;
@@ -2224,7 +2224,7 @@ p_atom_number(void)
     }
     String = Yap_PreAllocCodeSpace();
     if (String+1024 > (char *)AuxSp) {
-      s = String = Yap_ExpandPreAllocCodeSpace(0,NULL);
+      s = String = Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE);
       if (String + 1024 > (char *)AuxSp) {
 	/* crash in flames */
 	Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "allocating temp space in number_codes/2");
@@ -2493,7 +2493,7 @@ p_sub_atom_extract(void)
 
  expand_auxsp:
   {
-    char *String = Yap_ExpandPreAllocCodeSpace(len,NULL);
+    char *String = Yap_ExpandPreAllocCodeSpace(len, NULL, TRUE);
     if (String + 1024 > (char *)AuxSp) {
       /* crash in flames */
       Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "allocating temp space in sub_atom/5");
diff --git a/C/unify.c b/C/unify.c
index c57cbf138..a6a1ab2b2 100644
--- a/C/unify.c
+++ b/C/unify.c
@@ -18,7 +18,9 @@
 
 #include "absmi.h"
 
-STATIC_PROTO(Int    OCUnify_complex, (register CELL *, register CELL *, register CELL *));
+STD_PROTO(int   Yap_rational_tree_loop, (CELL *, CELL *, CELL **, CELL **));
+
+STATIC_PROTO(int    OCUnify_complex, (CELL *, CELL *, CELL *));
 STATIC_PROTO(int    OCUnify, (register CELL, register CELL));
 STATIC_PROTO(Int   p_ocunify, (void));
 #ifdef THREADED_CODE
@@ -28,32 +30,13 @@ STATIC_PROTO(void   InitReverseLookupOpcode, (void));
 
 /* support for rational trees and unification with occur checking */
 
-#if USE_SYSTEM_MALLOC
-#define address_to_visit_max (&to_visit_max)
-#define to_visit_base ((CELL **)AuxSp)
-
-#define TO_VISIT to_visit, to_visit_max
-int STD_PROTO(rational_tree_loop,(CELL *, CELL *, CELL **, CELL **));
-
-#else
-#define to_visit_max ((CELL **)TR+16)
-#define address_to_visit_max NULL
-#define to_visit_base ((CELL **)Yap_TrailTop)
-
-#define TO_VISIT to_visit
-int STD_PROTO(rational_tree_loop,(CELL *, CELL *, CELL **));
-
-#endif
+#define to_visit_base ((struct v_record *)AuxSp)
 
 int
-rational_tree_loop(CELL *pt0, CELL *pt0_end, CELL **to_visit
-#if USE_SYSTEM_MALLOC
-		   , CELL **to_visit_max
-#endif
-		   )
+Yap_rational_tree_loop(CELL *pt0, CELL *pt0_end, CELL **to_visit, CELL **to_visit_max)
 {
 
-loop:
+rtree_loop:
   while (pt0 < pt0_end) {
     register CELL *ptd0;
     register CELL d0;
@@ -69,7 +52,9 @@ loop:
       if (IsPairTerm(d0)) {
 	to_visit -= 3;
 	if (to_visit < to_visit_max) {
-	  to_visit = Yap_shift_visit(to_visit, address_to_visit_max);
+	  to_visit = Yap_shift_visit(to_visit, &to_visit_max);
+
+
 	}
 	to_visit[0] = pt0;
 	to_visit[1] = pt0_end;
@@ -91,7 +76,7 @@ loop:
 	}
 	to_visit -= 3;
 	if (to_visit < to_visit_max) {
-	  to_visit = Yap_shift_visit(to_visit, address_to_visit_max);
+	  to_visit = Yap_shift_visit(to_visit, &to_visit_max);
 	}
 	to_visit[0] = pt0;
 	to_visit[1] = pt0_end;
@@ -108,12 +93,12 @@ loop:
     derefa_body(d0, ptd0, rtree_loop_unk, rtree_loop_nvar);
   }
   /* Do we still have compound terms to visit */
-  if (to_visit < to_visit_max) {
+  if (to_visit < (CELL **)to_visit_base) {
     pt0 = to_visit[0];
     pt0_end = to_visit[1];
     *pt0 = (CELL)to_visit[2];
     to_visit += 3;
-    goto loop;
+    goto rtree_loop;
   }
   return FALSE;
 
@@ -125,56 +110,60 @@ cufail:
     *pt0 = (CELL)to_visit[2];
     to_visit += 3;
   }
-  return (TRUE);
+  return TRUE;
   
 }
 
 static inline int
 rational_tree(Term d0) {
-#if USE_SYSTEM_MALLOC
-  CELL  **to_visit_max = (CELL **)Yap_PreAllocCodeSpace(), **to_visit  = (CELL **)AuxSp;
-#else
-  CELL  **to_visit  = (CELL **)Yap_TrailTop;
-#endif
+  CELL  **to_visit_max = (CELL **)AuxBase, **to_visit  = (CELL **)AuxSp;
 
   if (IsPairTerm(d0)) {
     CELL *pt0 = RepPair(d0);
 
-    return rational_tree_loop(pt0-1, pt0+1, TO_VISIT);
+    return Yap_rational_tree_loop(pt0-1, pt0+1, to_visit, to_visit_max);
   } else if (IsApplTerm(d0)) {
     CELL *pt0 = RepAppl(d0);
     Functor f = (Functor)(*pt0);
 
     if (IsExtensionFunctor(f))
       return FALSE;
-    return rational_tree_loop(pt0, pt0+ArityOfFunctor(f), TO_VISIT);
+    return Yap_rational_tree_loop(pt0, pt0+ArityOfFunctor(f), to_visit, to_visit_max);
   } else
     return FALSE;
 }
 
-static Int 
-OCUnify_complex(register CELL *pt0, register CELL *pt0_end,
-	       register CELL *pt1
-)
+static int 
+OCUnify_complex(CELL *pt0, CELL *pt0_end, CELL *pt1)
 {
+#ifdef THREADS
+#undef Yap_REGS
+  register REGSTORE *regp = Yap_regp;
+#define Yap_REGS (*regp)
+#elif defined(SHADOW_REGS)
+#if defined(B) || defined(TR)
+  register REGSTORE *regp = &Yap_REGS;
 
-#if USE_SYSTEM_MALLOC
-  CELL  **to_visit_max = (CELL **)Yap_PreAllocCodeSpace(), **to_visit  = (CELL **)AuxSp;
-#else
-  CELL  **to_visit  = (CELL **)Yap_TrailTop;
+#define Yap_REGS (*regp)
+#endif /* defined(B) || defined(TR) || defined(HB) */
 #endif
 
-#if SHADOW_HB
-  register CELL *HBREG;
-  HBREG = HB;
-#endif
+#ifdef SHADOW_HB
+  register CELL *HBREG = HB;
+#endif /* SHADOW_HB */
 
- loop:
+  struct unif_record  *unif = (struct unif_record *)AuxBase;
+  struct v_record *to_visit  = (struct v_record *)AuxSp;
+#define unif_base ((struct unif_record *)AuxBase)
+
+loop:
   while (pt0 < pt0_end) {
-    register CELL *ptd0 = ++pt0;
-    register CELL d0 = *ptd0;
+    register CELL *ptd0 = pt0+1; 
+    register CELL d0;
 
     ++pt1;
+    pt0 = ptd0;
+    d0 = *ptd0;
     deref_head(d0, unify_comp_unk);
   unify_comp_nvar:
     {
@@ -184,93 +173,90 @@ OCUnify_complex(register CELL *pt0, register CELL *pt0_end,
       deref_head(d1, unify_comp_nvar_unk);
     unify_comp_nvar_nvar:
       if (d0 == d1) {
-	if (rational_tree_loop(pt0-1, pt0, TO_VISIT))
+	if (Yap_rational_tree_loop(pt0-1, pt0, (CELL **)to_visit, (CELL **)unif))
 	  goto cufail;
 	continue;
-      } if (IsPairTerm(d0)) {
+      }
+      if (IsPairTerm(d0)) {
 	if (!IsPairTerm(d1)) {
 	  goto cufail;
 	}
 	/* now link the two structures so that no one else will */
 	/* come here */
-	to_visit -= 5;
-	if (to_visit < to_visit_max) {
-	  to_visit = Yap_shift_visit(to_visit, address_to_visit_max);
+	/* store the terms to visit */
+	if (RATIONAL_TREES || pt0 < pt0_end) {
+	  to_visit --;
+#ifdef RATIONAL_TREES
+	  unif++;
+#endif
+	  if ((void *)to_visit < (void *)unif) {
+	    struct unif_record *urec = unif;
+	    to_visit = (struct v_record *)Yap_shift_visit((CELL **)to_visit, (CELL ***)&urec);
+	    unif = urec;
+	  }
+	  to_visit->start0 = pt0;
+	  to_visit->end0 = pt0_end;
+	  to_visit->start1 = pt1;
+#ifdef RATIONAL_TREES
+	  unif[-1].old = *pt0;
+	  unif[-1].ptr = pt0;
+	  *pt0 = d1;
+#endif
 	}
-	to_visit[0] = pt0;
-	to_visit[1] = pt0_end;
-	to_visit[2] = pt1;
-	/* we want unification of rational trees to fail */
-	to_visit[3] = (CELL *)*pt0;
-	to_visit[4] = (CELL *)*pt1;
-	*pt0 = TermFoundVar;
-	*pt1 = TermFoundVar;
 	pt0_end = (pt0 = RepPair(d0) - 1) + 2;
-	pt0_end = RepPair(d0) + 1;
 	pt1 = RepPair(d1) - 1;
 	continue;
       }
-      else if (IsApplTerm(d0)) {
+      if (IsApplTerm(d0)) {
 	register Functor f;
 	register CELL *ap2, *ap3;
 
-	/* store the terms to visit */
-	ap2 = RepAppl(d0);
-	f = (Functor) (*ap2);
 	if (!IsApplTerm(d1)) {
 	  goto cufail;
 	}
+	/* store the terms to visit */
+	ap2 = RepAppl(d0);
 	ap3 = RepAppl(d1);
+	f = (Functor) (*ap2);
 	/* compare functors */
-	if (f != (Functor) *ap3) {
+	if (f != (Functor) *ap3)
 	  goto cufail;
-	}
 	if (IsExtensionFunctor(f)) {
-	  switch((CELL)f) {
-	  case (CELL)FunctorDBRef:
-	    if (d0 == d1) continue;
-	    goto cufail;
-	  case (CELL)FunctorLongInt:
-	    if (ap2[1] == ap3[1]) continue;
-	    goto cufail;
-	  case (CELL)FunctorDouble:
-	    if (FloatOfTerm(d0) == FloatOfTerm(d1)) continue;
-	    goto cufail;
-#ifdef USE_GMP
-	  case (CELL)FunctorBigInt:
-	    if (mpz_cmp(Yap_BigIntOfTerm(d0),Yap_BigIntOfTerm(d1)) == 0) continue;
-	    goto cufail;
-#endif /* USE_GMP */
-	  default:
-	    goto cufail;
-	  }
+	  if (unify_extension(f, d0, ap2, d1))
+	    continue;
+	  goto cufail;
 	}
 	/* now link the two structures so that no one else will */
 	/* come here */
-	to_visit -= 5;
-	if (to_visit < to_visit_max) {
-	  to_visit = Yap_shift_visit(to_visit, address_to_visit_max);
+	/* store the terms to visit */
+	if (RATIONAL_TREES || pt0 < pt0_end) {
+	  to_visit --;
+#ifdef RATIONAL_TREES
+	  unif++;
+#endif
+	  if ((void *)to_visit < (void *)unif) {
+	    struct unif_record *urec = unif;
+	    to_visit = (struct v_record *)Yap_shift_visit((CELL **)to_visit, (CELL ***)&urec);
+	    unif = urec;
+	  }
+	  to_visit->start0 = pt0;
+	  to_visit->end0 = pt0_end;
+	  to_visit->start1 = pt1;
+#ifdef RATIONAL_TREES
+	  unif[-1].old = *pt0;
+	  unif[-1].ptr = pt0;
+	  *pt0 = d1;
+#endif
 	}
-	to_visit[0] = pt0;
-	to_visit[1] = pt0_end;
-	to_visit[2] = pt1;
-	to_visit[3] = (CELL *)*pt0;
-	to_visit[4] = (CELL *)*pt1;
-	*pt0 = TermFoundVar;
-	*pt1 = TermFoundVar;
 	d0 = ArityOfFunctor(f);
 	pt0 = ap2;
 	pt0_end = ap2 + d0;
 	pt1 = ap3;
 	continue;
-      } else {
-	if (d0 == d1)
-	  continue;
-	else goto cufail;
       }
+      goto cufail;
 
       derefa_body(d1, ptd1, unify_comp_nvar_unk, unify_comp_nvar_nvar);
-      
       /* d1 and pt2 have the unbound value, whereas d0 is bound */
       BIND_GLOBAL(ptd1, d0, bind_ocunify1);
 #ifdef COROUTINING
@@ -278,18 +264,19 @@ OCUnify_complex(register CELL *pt0, register CELL *pt0_end,
       if (ptd1 < H0) Yap_WakeUp(ptd1);
     bind_ocunify1:
 #endif
-      if (rational_tree_loop(ptd1-1, ptd1, TO_VISIT))
+      if (Yap_rational_tree_loop(ptd1-1, ptd1, (CELL **)to_visit, (CELL **)unif))
 	goto cufail;
       continue;
-
     }
 
     derefa_body(d0, ptd0, unify_comp_unk, unify_comp_nvar);
+    /* first arg var */
     {
       register CELL d1;
-      register CELL *ptd1 = NULL;
+      register CELL *ptd1;
 
-      d1 = *(ptd1 = pt1);
+      ptd1 = pt1;
+      d1 = ptd1[0];
       /* pt2 is unbound */
       deref_head(d1, unify_comp_var_unk);
     unify_comp_var_nvar:
@@ -300,7 +287,7 @@ OCUnify_complex(register CELL *pt0, register CELL *pt0_end,
       if (ptd0 < H0) Yap_WakeUp(ptd0);
     bind_ocunify2:
 #endif
-      if (rational_tree_loop(ptd0-1, ptd0, TO_VISIT))
+      if (Yap_rational_tree_loop(ptd0-1, ptd0, (CELL **)to_visit, (CELL **)unif))
 	goto cufail;
       continue;
 
@@ -311,37 +298,44 @@ OCUnify_complex(register CELL *pt0, register CELL *pt0_end,
   }
   /* Do we still have compound terms to visit */
   if (to_visit < to_visit_base) {
-    pt0 = to_visit[0];
-    pt0_end = to_visit[1];
-    pt1 = to_visit[2];
-    *pt0 = (CELL)to_visit[3];
-    *pt1 = (CELL)to_visit[4];
-    to_visit += 5;
+    pt0 = to_visit->start0;
+    pt0_end = to_visit->end0;
+    pt1 = to_visit->start1;
+    to_visit++;
     goto loop;
   }
-  /* successful exit */
-  return (TRUE);
+#ifdef RATIONAL_TREES
+  /* restore bindigs */
+  while (unif-- != unif_base) {
+    CELL *pt0;
+
+    pt0 = unif->ptr;
+    *pt0 = unif->old;
+  }
+#endif
+  return TRUE;
 
 cufail:
-  /* failure */
-  while (to_visit < to_visit_base) {
+#ifdef RATIONAL_TREES
+  /* restore bindigs */
+  while (unif-- != unif_base) {
     CELL *pt0;
-    pt0 = to_visit[0];
-    pt1 = to_visit[2];
-    *pt0 = (CELL)to_visit[3];
-    *pt1 = (CELL)to_visit[4];
-    to_visit += 5;
+
+    pt0 = unif->ptr;
+    *pt0 = unif->old;
   }
-  /* failure */
-  return (FALSE);
-#if SHADOW_REGS
+#endif
+  return FALSE;
+#ifdef THREADS
+#undef Yap_REGS
+#define Yap_REGS (*Yap_regp)  
+#elif defined(SHADOW_REGS)
 #if defined(B) || defined(TR)
 #undef Yap_REGS
-#if PUSH_REGS
-#define Yap_REGS (*Yap_regp)
-#endif
 #endif /* defined(B) || defined(TR) */
 #endif
+#undef unif_base
+#undef to_visit_base
 }
 
 static int 
diff --git a/C/utilpreds.c b/C/utilpreds.c
index fa8daaa9c..89682234c 100644
--- a/C/utilpreds.c
+++ b/C/utilpreds.c
@@ -406,7 +406,7 @@ handle_cp_overflow(int res, tr_fr_ptr TR0, UInt arity, Term t)
       Yap_Error_Size = 0L;
       if (size > 4*1024*1024)
 	size = 4*1024*1024;
-      if (!Yap_ExpandPreAllocCodeSpace(size,NULL)) {
+      if (!Yap_ExpandPreAllocCodeSpace(size, NULL, TRUE)) {
 	Yap_Error(OUT_OF_AUXSPACE_ERROR, TermNil, Yap_ErrorMessage);
 	return 0L;
       }
@@ -736,7 +736,7 @@ expand_vts(void)
     /* Aux space overflow */
     if (expand > 4*1024*1024)
       expand = 4*1024*1024;
-    if (!Yap_ExpandPreAllocCodeSpace(expand, NULL)) {
+    if (!Yap_ExpandPreAllocCodeSpace(expand, NULL, TRUE)) {
       return FALSE;
     }
   } else {
@@ -1429,7 +1429,7 @@ p_non_singletons_in_term(void)	/* non_singletons in term t		 */
     if (out != 0L) {
       return Yap_unify(ARG3,out);
     } else {
-      if (!Yap_ExpandPreAllocCodeSpace(0, NULL)) {
+      if (!Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE)) {
 	Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "overflow in singletons");
 	return FALSE;
       }
@@ -1577,7 +1577,7 @@ p_ground(void)			/* ground(+T)		 */
       }
     }
     if (out < 0) {
-      if (!Yap_ExpandPreAllocCodeSpace(0, NULL)) {
+      if (!Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE)) {
 	Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "overflow in ground");
 	return FALSE;
       }      
@@ -2206,7 +2206,7 @@ p_term_hash(void)
   while (TRUE) {
     CELL *ar = hash_complex_term(&t1-1, &t1, depth, H, FALSE);
     if (ar == (CELL *)-1) {
-      if (!Yap_ExpandPreAllocCodeSpace(0, NULL)) {
+      if (!Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE)) {
 	Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "overflow in term_hash");
 	return FALSE;
       } 
@@ -2264,7 +2264,7 @@ p_instantiated_term_hash(void)
   while (TRUE) {
     CELL *ar = hash_complex_term(&t1-1, &t1, depth, H, TRUE);
     if (ar == (CELL *)-1) {
-      if (!Yap_ExpandPreAllocCodeSpace(0, NULL)) {
+      if (!Yap_ExpandPreAllocCodeSpace(0, NULL, TRUE)) {
 	Yap_Error(OUT_OF_AUXSPACE_ERROR, ARG1, "overflow in term_hash");
 	return FALSE;
       } 
diff --git a/C/write.c b/C/write.c
index 10b7549dc..c6d1fc1d8 100644
--- a/C/write.c
+++ b/C/write.c
@@ -570,7 +570,7 @@ writeTerm(Term t, int p, int depth, int rinfixarg, struct write_globs *wglb, str
 	  while (s+3+mpz_sizeinbase(big, 10) >= (char *)AuxSp) {
 #if USE_SYSTEM_MALLOC
 	    /* may require stack expansion */
-	    if (!Yap_ExpandPreAllocCodeSpace(3+mpz_sizeinbase(big, 10),NULL)) {
+	    if (!Yap_ExpandPreAllocCodeSpace(3+mpz_sizeinbase(big, 10), NULL, TRUE)) {
 	      s = NULL;
 	      break;
 	    }
diff --git a/H/Heap.h b/H/Heap.h
index 30d039b1a..feedccaeb 100644
--- a/H/Heap.h
+++ b/H/Heap.h
@@ -812,15 +812,13 @@ extern struct various_codes *Yap_heap_regs;
 UInt STD_PROTO(Yap_givemallinfo, (void));
 #endif
 
-ADDR    STD_PROTO(Yap_ExpandPreAllocCodeSpace, (UInt, void *));
+ADDR    STD_PROTO(Yap_ExpandPreAllocCodeSpace, (UInt, void *, int));
 #define Yap_ReleasePreAllocCodeSpace(x)
 ADDR    STD_PROTO(Yap_InitPreAllocCodeSpace, (void));
 EXTERN inline ADDR
-Yap_PreAllocCodeSpace(void)
+Yap_PreAllocCodeSpace(void) 
 {
-  ADDR ptr = ScratchPad.ptr;
-  if (ptr) return ptr;
-  return Yap_InitPreAllocCodeSpace();
+  return AuxBase;
 }
 
 #endif /* HEAP_H */
diff --git a/H/Regs.h b/H/Regs.h
index f85e56a2f..6db618db6 100644
--- a/H/Regs.h
+++ b/H/Regs.h
@@ -105,6 +105,7 @@ typedef struct
     CELL  *ENV_;		/* 1 current environment                      */
     CELL  *ASP_;		/* 8 top of local       stack                 */
     CELL  *LCL0_;		/* 3 local stack base                         */
+    ADDR   AuxBase_;		/* 9 Auxiliary base  pointer                  */
     CELL  *AuxSp_;		/* 9 Auxiliary stack pointer                  */
     ADDR   AuxTop_;		/* 10 Auxiliary stack top                     */
 /* visualc*/
@@ -697,6 +698,7 @@ EXTERN inline void restore_B(void) {
 
 #endif
 
+#define	AuxBase       Yap_REGS.AuxBase_
 #define	AuxSp         Yap_REGS.AuxSp_
 #define	AuxTop        Yap_REGS.AuxTop_
 #define TopB          Yap_REGS.TopB_
diff --git a/H/absmi.h b/H/absmi.h
index fa222c236..0a2096b0f 100644
--- a/H/absmi.h
+++ b/H/absmi.h
@@ -1083,17 +1083,21 @@ Macros to check the limits of stacks
 #define save_hb()
 #endif
 
-#if defined(IN_ABSMI_C) || defined(IN_UNIFY_C)
+typedef struct unif_record {
+  CELL *ptr;
+  Term old;
+} unif_record;
 
-typedef struct u_record {
+typedef struct v_record {
   CELL *start0;
   CELL *end0;
   CELL *start1;
   Term old;
-} unif_record;
+} v_record;
+
+#if defined(IN_ABSMI_C) || defined(IN_UNIFY_C)
 
 static int 
-
 IUnify_complex(CELL *pt0, CELL *pt0_end, CELL *pt1)
 {
 #ifdef THREADS
@@ -1112,16 +1116,10 @@ IUnify_complex(CELL *pt0, CELL *pt0_end, CELL *pt1)
   register CELL *HBREG = HB;
 #endif /* SHADOW_HB */
 
-#ifdef USE_SYSTEM_MALLOC
-  struct u_record  *to_visit_max = (struct u_record *)Yap_PreAllocCodeSpace(), *to_visit  = (struct u_record *)AuxSp;
-#define address_to_visit_max (&to_visit_max)
-#define to_visit_base ((CELL **)AuxSp)
-#else
-  struct u_record *to_visit  = (struct u_record *)Yap_TrailTop;
-#define to_visit_max ((struct u_record *)TR+16)
-#define address_to_visit_max NULL
-#define to_visit_base ((struct u_record *)Yap_TrailTop)
-#endif
+  struct unif_record  *unif = (struct unif_record *)AuxBase;
+  struct v_record *to_visit  = (struct v_record *)AuxSp;
+#define unif_base ((struct unif_record *)AuxBase)
+#define to_visit_base ((struct v_record *)AuxSp)
 
 loop:
   while (pt0 < pt0_end) {
@@ -1145,31 +1143,28 @@ loop:
 	if (!IsPairTerm(d1)) {
 	  goto cufail;
 	}
-#ifdef RATIONAL_TREES
 	/* now link the two structures so that no one else will */
 	/* come here */
-	to_visit -- ;
-	if (to_visit < to_visit_max) {
-	  to_visit = (struct u_record *)Yap_shift_visit((CELL **)to_visit, (CELL ***)address_to_visit_max);
-	}
-	to_visit->start0 = pt0;
-	to_visit->end0 = pt0_end;
-	to_visit->start1 = pt1;
-	to_visit->old = *pt0;
-	*pt0 = d1;
-#else
 	/* store the terms to visit */
-	if (pt0 < pt0_end) {
+	if (RATIONAL_TREES || pt0 < pt0_end) {
 	  to_visit --;
-	  if (to_visit < to_visit_max) {
-	    to_visit = (struct u_record *)Yap_shift_visit((CELL **)to_visit, (CELL ***)address_to_visit_max);
+#ifdef RATIONAL_TREES
+	  unif++;
+#endif
+	  if ((void *)to_visit < (void *)unif) {
+	    struct unif_record *urec = unif;
+	    to_visit = (struct v_record *)Yap_shift_visit((CELL **)to_visit, (CELL ***)&urec);
+	    unif = urec;
 	  }
 	  to_visit->start0 = pt0;
 	  to_visit->end0 = pt0_end;
 	  to_visit->start1 = pt1;
-	}
-
+#ifdef RATIONAL_TREES
+	  unif[-1].old = *pt0;
+	  unif[-1].ptr = pt0;
+	  *pt0 = d1;
 #endif
+	}
 	pt0_end = (pt0 = RepPair(d0) - 1) + 2;
 	pt1 = RepPair(d1) - 1;
 	continue;
@@ -1193,30 +1188,28 @@ loop:
 	    continue;
 	  goto cufail;
 	}
-#ifdef RATIONAL_TREES
 	/* now link the two structures so that no one else will */
 	/* come here */
-	to_visit --;
-	if (to_visit < to_visit_max) {
-	  to_visit = (struct u_record *)Yap_shift_visit((CELL **)to_visit, (CELL ***)address_to_visit_max);
-	}
-	to_visit->start0 = pt0;
-	to_visit->end0 = pt0_end;
-	to_visit->start1 = pt1;
-	to_visit->old = *pt0;
-	*pt0 = d1;
-#else
 	/* store the terms to visit */
-	if (pt0 < pt0_end) {
+	if (RATIONAL_TREES || pt0 < pt0_end) {
 	  to_visit --;
-	  if (to_visit < to_visit_max) {
-	    to_visit = Yap_shift_visit(to_visit, address_to_visit_max);
+#ifdef RATIONAL_TREES
+	  unif++;
+#endif
+	  if ((void *)to_visit < (void *)unif) {
+	    struct unif_record *urec = unif;
+	    to_visit = (struct v_record *)Yap_shift_visit((CELL **)to_visit, (CELL ***)&urec);
+	    unif = urec;
 	  }
 	  to_visit->start0 = pt0;
 	  to_visit->end0 = pt0_end;
 	  to_visit->start1 = pt1;
-	}
+#ifdef RATIONAL_TREES
+	  unif[-1].old = *pt0;
+	  unif[-1].ptr = pt0;
+	  *pt0 = d1;
 #endif
+	}
 	d0 = ArityOfFunctor(f);
 	pt0 = ap2;
 	pt0_end = ap2 + d0;
@@ -1254,23 +1247,28 @@ loop:
     pt0 = to_visit->start0;
     pt0_end = to_visit->end0;
     pt1 = to_visit->start1;
-#ifdef RATIONAL_TREES
-    *pt0 = to_visit->old;
-#endif
-    to_visit ++;
+    to_visit++;
     goto loop;
   }
+#ifdef RATIONAL_TREES
+  /* restore bindigs */
+  while (unif-- != unif_base) {
+    CELL *pt0;
+
+    pt0 = unif->ptr;
+    *pt0 = unif->old;
+  }
+#endif
   return TRUE;
 
 cufail:
 #ifdef RATIONAL_TREES
-  /* failure */
-  while (to_visit < to_visit_base) {
+  /* restore bindigs */
+  while (unif-- != unif_base) {
     CELL *pt0;
 
-    pt0 = to_visit->start0;
-    *pt0 = to_visit->old;
-    to_visit ++;
+    pt0 = unif->ptr;
+    *pt0 = unif->old;
   }
 #endif
   return FALSE;
@@ -1285,14 +1283,8 @@ cufail:
 }
 
 /*  don't pollute name space */
-#if USE_SYSTEM_MALLOC
-#undef address_to_visit_max
 #undef to_visit_base
-#else
-#undef to_visit_max
-#undef address_to_visit_max
-#undef to_visit_base
-#endif
+#undef unif_base
 
 
 #endif