diff --git a/C/tracer.c b/C/tracer.c
index 74da2a1bc..d8e686db1 100644
--- a/C/tracer.c
+++ b/C/tracer.c
@@ -52,17 +52,7 @@ send_tracer_message(char *start, char *name, Int arity, char *mname, CELL *args)
     if (args) {
       for (i= 0; i < arity; i++) {
 	if (i > 0) fprintf(GLOBAL_stderr, ",");
-#if DEBUG
-#if COROUTINING
-	Yap_Portray_delays = TRUE;
-#endif
-#endif
-	Yap_plwrite(args[i], NULL, 15, Handle_vars_f, 1200);
-#if DEBUG
-#if COROUTINING
-	Yap_Portray_delays = FALSE;
-#endif
-#endif
+	Yap_plwrite(args[i], NULL, 15, Handle_vars_f|AttVar_Portray_f, 1200);
       }
       if (arity) {
 	fprintf(GLOBAL_stderr, ")");
diff --git a/C/write.c b/C/write.c
index 93b8f30c6..0c078ad93 100644
--- a/C/write.c
+++ b/C/write.c
@@ -1014,13 +1014,15 @@ writeTerm(Term t, int p, int depth, int rinfixarg, struct write_globs *wglb, str
 	wrputc(')', wglb->stream);
 	lastw = separator;
       }
-      /* avoid quoting commas */
-      if (strcmp(RepAtom(atom)->StrOfAE,","))
-	putAtom(atom, wglb->Quote_illegal, wglb);
-      else {
+      /* avoid quoting commas and bars */
+      if (!strcmp(RepAtom(atom)->StrOfAE,",")) {
 	wrputc(',', wglb->stream);
 	lastw = separator;
-      }
+      } else if (!strcmp(RepAtom(atom)->StrOfAE,"|")) {
+	wrputc('|', wglb->stream);
+	lastw = separator;
+      } else
+	putAtom(atom, wglb->Quote_illegal, wglb);
       if (bracket_right) {
 	wrputc('(', wglb->stream);
 	lastw = separator;
diff --git a/pl/sort.yap b/pl/sort.yap
index cbbc7ca1e..5b09c4379 100644
--- a/pl/sort.yap
+++ b/pl/sort.yap
@@ -54,6 +54,27 @@ length(L, M) :-
           M is N + 1, NL  = [_|L], '$$_length2'(L, O, M) ).
 
 sort(L,O) :-
+	'$skip_list'(L,NL,RL),
+	( RL == [] -> true ;
+	  var(RL) -> '$do_error'(instantiation_error,sort(L,O)) ;
+	 '$do_error'(type_error(list,L),sort(L,O))
+	),
+	(
+         nonvar(O)
+        ->
+	 (
+	   O == []
+         ->
+           L == []
+	 ;
+	   '$skip_list'(O,NO,RO),
+	   ( RO == [] -> NO =< NL ;
+	     var(RO) -> NO =< NL ;
+	     '$do_error'(type_error(list,O),sort(L,O))
+	   )
+         )
+        ; true
+	),
 	'$sort'(L,O).
 
 msort(L,O) :-
diff --git a/pl/threads.yap b/pl/threads.yap
index 2d84b7692..cf856b671 100644
--- a/pl/threads.yap
+++ b/pl/threads.yap
@@ -209,7 +209,7 @@ thread_create(Goal, Id, Options) :-
 % vsc: ?????
 thread_defaults(Defaults) :-
 	nonvar(Defaults), !,
-	'$do_error'(uninstantion_error(Defaults), thread_defaults(Defaults)).
+	'$do_error'(uninstantiation_error(Defaults), thread_defaults(Defaults)).
 thread_defaults([stack(Stack), trail(Trail), system(System), detached(Detached), at_exit(AtExit)]) :-
 	recorded('$thread_defaults',[Stack, Trail, System, Detached, AtExit], _).
 
diff --git a/pl/utils.yap b/pl/utils.yap
index 83306a5d3..28e519b35 100644
--- a/pl/utils.yap
+++ b/pl/utils.yap
@@ -93,13 +93,13 @@
  '$check_op_name'(_,_,',',G) :- !,
 	  '$do_error'(permission_error(modify,operator,','),G).
  '$check_op_name'(_,_,'[]',G) :- !,
-	  '$do_error'(permispsion_error(create,operator,'[]'),G).
+	  '$do_error'(permission_error(create,operator,'[]'),G).
  '$check_op_name'(_,_,'{}',G) :- !,
 	  '$do_error'(permission_error(create,operator,'{}'),G).
  '$check_op_name'(P,T,'|',G) :-
 	 (
 	  integer(P),
-	  P < 1001
+	  P < 1001, P > 0
 	 ;
 	  atom_codes(T,[_,_])
 	 ), !,