diff --git a/C/terms.c b/C/terms.c
index e6230f90e..3e325f01e 100644
--- a/C/terms.c
+++ b/C/terms.c
@@ -981,16 +981,8 @@ static Term bind_vars_in_complex_term(CELL * pt0_, CELL * pt0_end_ USES_REGS) {
   *ptd0 = TermFoundVar;
   /* next make sure noone will see this as a variable again */
   if (TR > (tr_fr_ptr)LOCAL_TrailTop - 256) {
-    /* Trail overflow */
-    if (!Yap_growtrail((TR - TR0) * sizeof(tr_fr_ptr *), true)) {
-      while (to_visit > to_visit0) {
-       to_visit--;
-       CELL *ptd0 = to_visit->ptd0;
-       *ptd0 = to_visit->d0;
-     }
      goto trail_overflow;
    }
- }
  TrailTerm(TR++) = (CELL)ptd0;
 
  END_WALK();
@@ -1043,41 +1035,42 @@ if (found_module && t != t0) {
 return Yap_unify(ARG2, t) && Yap_unify(ARG3, out);
 }
 
-#define FOUND_VAR_AGAIN()			\
-if (d0 == TermFoundVar) {			\
-  CELL *pt2 = pt0;				\
-  while (IsVarTerm(*pt2))			\
-    pt2 = (CELL *)(*pt2);			\
-  HR[1] = AbsPair(HR + 2);			\
-  HR[0] = (CELL)pt2;				\
-  HR += 2;					\
-  *pt2 = TermRefoundVar;			\
-}
+#define FOUND_VAR_AGAIN()   \
+  if (d0 == TermFoundVar)   \
+  {                         \
+    HR[0] = (CELL)ptd0;     \
+    HR[1] = AbsPair(HR + 2); \
+    HR += 2;                \
+    *ptd0 = TermRefoundVar; \
+  }
 
 static Term non_singletons_in_complex_term(CELL * pt0_,
   CELL * pt0_end_ USES_REGS) {
-  HB = (CELL *)ASP;
-  CELL output = AbsPair(HR);
 
   WALK_COMPLEX_TERM__({}, {}, FOUND_VAR_AGAIN());
   /* do or pt2 are unbound  */
-  YapBind(ptd0, TermFoundVar);
-  goto restart;
+  *ptd0 = TermFoundVar;
+  /* next make sure noone will see this as a variable again */
+  if (TR > (tr_fr_ptr)LOCAL_TrailTop - 256)
+  {
+    goto trail_overflow;
+  }
+  TrailTerm(TR++) = (CELL)ptd0;
   END_WALK();
 
   clean_tr(TR0 PASS_REGS);
 
   pop_text_stack(lvl);
-  HB = (CELL *)B->cp_b;
   if (HR != InitialH) {
     /* close the list */
     HR[-1] = Deref(ARG2);
-    return output;
+    return AbsPair(InitialH);
   } else {
     return ARG2;
   }
 
   def_aux_overflow();
+  def_trail_overflow();
 }
 
 static Int p_non_singletons_in_term(
@@ -1094,7 +1087,7 @@ static Int p_non_singletons_in_term(
     } else {
       out = non_singletons_in_complex_term(&(t)-1, &(t)PASS_REGS);
     }
-    return out;
+    return Yap_unify(ARG3,out);
  }
 
 static Term numbervar(Int me USES_REGS) {
diff --git a/C/utilpreds.c b/C/utilpreds.c
index 092ea2ced..89d18adff 100644
--- a/C/utilpreds.c
+++ b/C/utilpreds.c
@@ -395,9 +395,9 @@ int Yap_copy_complex_term(register CELL *pt0, register CELL *pt0_end,
 	RESET_VARIABLE(ptf);
 	*ptd0 = (CELL)ptf;
 	ptf++;
-	if ((ADDR)TR > LOCAL_TrailTop - 16)
+  TrailTerm(TR++) = (CELL)ptd0;
+  if ((ADDR)TR > LOCAL_TrailTop - 16)
 	  goto trail_overflow;
-
     }
   }
   
@@ -521,7 +521,7 @@ CopyTerm(Term inp, UInt arity, int share, int newattvs USES_REGS) {
 Term
 Yap_CopyTerm(Term inp) {
   CACHE_REGS
-    return CopyTerm(inp, 0, TRUE, TRUE PASS_REGS);
+    return CopyTerm(inp, 0, false, TRUE PASS_REGS);
 }
 
 Term
@@ -533,7 +533,7 @@ Yap_CopyTermNoShare(Term inp) {
 static Int
 p_copy_term( USES_REGS1 )		/* copy term t to a new instance  */
 {
-  Term t = CopyTerm(ARG1, 2, TRUE, TRUE PASS_REGS);
+  Term t = CopyTerm(ARG1, 2, false, TRUE PASS_REGS);
   if (t == 0L)
     return FALSE;
   /* be careful, there may be a stack shift here */
diff --git a/pl/debug.yap b/pl/debug.yap
index ca648226f..cc6abede9 100644
--- a/pl/debug.yap
+++ b/pl/debug.yap
@@ -16,7 +16,7 @@
 *************************************************************************/
 
 
-:- system_module( '$_debug', [], ['$trace_query'/4,
+:- system_module( '$_debug', [], ['$trace_plan'/4,
         '$init_debugger'/0,
         '$skipeol'/1]).
 
@@ -254,7 +254,7 @@ be lost.
    *
    * The debugger is an interpreter. with main predicates:
    * - $trace: this is the API
-   * - $trace_query: reduce a query to a goal
+   * - $trace_plan: reduce a query to a goal
    * - $trace_goal: execute:
    *    + using the source, Luke
    *    + hooking into the WAM procedure call mechanism
@@ -308,7 +308,7 @@ be lost.
      '$execute_nonstop'(G,Mod).
 '$trace'(Mod:G) :-
     '$$save_by'(CP),
-    '$trace_query'(G, Mod, CP, G, EG),
+    '$trace_plan'(G, Mod, CP, G, EG),
     gated_call(
 	'$debugger_io',
 	EG,
@@ -415,42 +415,54 @@ be lost.
 
 
 '$trace_meta_call'( G, M, CP ) :-
-    '$trace_query'(G, M, CP, G, EG ),
+    '$trace_plan'(G, M, CP, G, EG ),
     call(EG).
 
-%% @pred '$trace_query'( +G, +M, +CP, +Expanded)
+%% @pred '$trace_plan'( +G, +M, +CP, +Expanded)
 %
 % debug a complex query
 %
-'$trace_query'(V, M, _CP, _, call(M:V)) :-
+'$trace_plan'(V, M, _CP, _, call(M:V)) :-
     var(V), !.
-'$trace_query'(!, _, CP, _, '$$cut_by'(CP)) :-
+'$trace_plan'(!, _, CP, _, '$$cut_by'(CP)) :-
     !.
-'$trace_query'('$cut_by'(M), _, _, _, '$$cut_by'(M)) :-
+'$trace_plan'('$cut_by'(M), _, _, _, '$$cut_by'(M)) :-
     !.
-'$trace_query'('$$cut_by'(M), _, _, _, '$$cut_by'(M)) :-
+'$trace_plan'('$$cut_by'(M), _, _, _, '$$cut_by'(M)) :-
     !.
-'$trace_query'(true, _, _, _, true) :- !.
-'$trace_query'(fail, _, _, _, '$trace'(fail)) :- !.
-'$trace_query'(M:G, _, CP,S, Expanded) :-
-    !,
-    '$yap_strip_module'(M:G, M0, G0),
-    '$trace_query'(G0, M0, CP,S, Expanded ).
-'$trace_query'((A,B), M, CP, S, (EA,EB)) :- !,
-    '$trace_query'(A, M, CP, S, EA),
-    '$trace_query'(B, M, CP, S, EB).
-'$trace_query'((A->B), M, CP, S, (EA->EB)) :- !,
-    '$trace_query'(A, M, CP, S, EA),
-    '$trace_query'(B, M, CP, S, EB).
-'$trace_query'((A;B), M, CP, S, (EA;EB)) :- !,
-	'$trace_query'(A, M, CP, S, EA),
-	'$trace_query'(B, M, CP, S, EB).
-'$trace_query'((A|B), M, CP, S, (EA|EB)) :- !,
-	'$trace_query'(A, M, CP, S, EA),
-	'$trace_query'(B, M, CP, S, EB).
-'$trace_query'((\+ A), M, CP, S, (\+ EA)) :- !,
-	'$trace_query'(A, M, CP, S, EA).
-'$trace_query'(G, M, _CP, _, (
+'$trace_plan'(true, _, _, _, true) :- !.
+'$trace_plan'(fail, _, _, _, '$trace'(fail)) :- !.
+'$trace_plan'((A,B), M, CP, S, (EA,EB)) :- !,
+    '$trace_plan'(A, M, CP, S, EA),
+    '$trace_plan'(B, M, CP, S, EB).
+'$trace_plan'((A->B), M, CP, S, (EA->EB)) :- !,
+    '$trace_plan'(A, M, CP, S, EA),
+    '$trace_plan'(B, M, CP, S, EB).
+'$trace_plan'((A;B), M, CP, S, (EA;EB)) :- !,
+	'$trace_plan'(A, M, CP, S, EA),
+	'$trace_plan'(B, M, CP, S, EB).
+'$trace_plan'((A|B), M, CP, S, (EA|EB)) :- !,
+	'$trace_plan'(A, M, CP, S, EA),
+	'$trace_plan'(B, M, CP, S, EB).
+	'$trace_plan'(C, M, CP, S, EC),
+'$trace_plan'((A->*B), M, CP, S, (EA->EB)) :- !,
+	'$trace_plan'(A, M, CP, S, EA),
+	'$trace_plan'(B, M, CP, S, EB).
+'$trace_plan'((A->*B;C), M, CP, S, (EA->EB;EC)) :- !,
+	'$trace_plan'(A, M, CP, S, EA),
+	'$trace_plan'(B, M, CP, S, EB),
+	'$trace_plan'(C, M, CP, S, EC).
+'$trace_plan'(if(A,B,C), M, CP, S, (EA->EB;EC)) :- !,
+	'$trace_plan'(A, M, CP, S, EA),
+	'$trace_plan'(B, M, CP, S, EB),
+	'$trace_plan'(C, M, CP, S, EC).
+'$trace_plan'((\+ A), M, CP, S, ( EA -> fail ; true)) :- !,
+	'$trace_plan'(A, M, CP, S, EA).
+'$trace_plan'(once(A), M, CP, S, ( EA ->  true)) :- !,
+	'$trace_plan'(A, M, CP, S, EA).
+'$trace_plan'(ignore(A), M, CP, S, ( EA -> true; true)) :- !,
+	'$trace_plan'(A, M, CP, S, EA).
+'$trace_plan'(G, M, _CP, _, (
         % spy a literal
 	'$id_goal'(L),
         catch(
@@ -487,9 +499,9 @@ be lost.
 	).
 % meta system
 '$trace_goal'(G, M, GoalNumber, H) :-
-        '$is_metapredicate'(G, prolog),
-        !,
-        '$debugger_expand_meta_call'(M:G, [], G1),
+    '$is_metapredicate'(G, prolog),
+    !,
+    '$debugger_expand_meta_call'(M:G, [], G1),
 	strip_module(G1, MF, NG),
 	gated_call(
 		   '$enter_trace'(GoalNumber, G, M, H),
@@ -604,7 +616,7 @@ be lost.
     '$$save_by'(CP),
     clause(M:G, Cl, _),
     '$retry_clause'(GoalNumber, G, M, Info, X),
-    '$trace_query'(Cl, M, CP, Cl, ECl),
+    '$trace_plan'(Cl, M, CP, Cl, ECl),
     '$execute0'(ECl,M).
 
 '$creep_step'(GoalNumber, G, M, Info) :-
@@ -654,7 +666,7 @@ be lost.
 
 
 %%% - abort: forward throw while the call is newer than goal
-%% @pred '$re_trace_query'( Exception, +Goal, +Mod, +GoalID )
+%% @pred '$re_trace_plan'( Exception, +Goal, +Mod, +GoalID )
 %
 % debugger code for exceptions. Recognised cases are:
 %   - abort always forwarded
@@ -1046,10 +1058,10 @@ be lost.
 '$cps'([]).
 
 
-'$debugger_skip_trace_query'([CP|CPs],CPs1) :-
-	yap_hacks:choicepoint(CP,_,prolog,'$trace_query',4,(_;_),_), !,
-	'$debugger_skip_trace_query'(CPs,CPs1).
-'$debugger_skip_trace_query'(CPs,CPs).
+'$debugger_skip_trace_plan'([CP|CPs],CPs1) :-
+	yap_hacks:choicepoint(CP,_,prolog,'$trace_plan',4,(_;_),_), !,
+	'$debugger_skip_trace_plan'(CPs,CPs1).
+'$debugger_skip_trace_plan'(CPs,CPs).
 
 '$debugger_skip_traces'([CP|CPs],CPs1) :-
 	yap_hacks:choicepoint(CP,_,prolog,'$port',4,(_;_),_), !,
diff --git a/pl/top.yap b/pl/top.yap
index 13197f25c..3f84a9c56 100644
--- a/pl/top.yap
+++ b/pl/top.yap
@@ -295,7 +295,7 @@ live :-
      '$write_answer'(Vs, LGs, Written),
 	  '$write_query_answer_true'(Written),
 	  (
-	   '$prompt_alternatives_on'(determinism), CP == NCP, DCP = 0
+	   yap_flag(prompt_alternatives_on,determinism), CP == NCP, DCP = 0
 	   ->
 	   format(user_error, '.~n', []),
 	   !