diff --git a/packages/ProbLog/problog_learning_lbdd.yap b/packages/ProbLog/problog_learning_lbdd.yap
index 2f6860d4d..a68b2f199 100644
--- a/packages/ProbLog/problog_learning_lbdd.yap
+++ b/packages/ProbLog/problog_learning_lbdd.yap
@@ -624,7 +624,7 @@ init_one_query(QueryID,Query,Type) :-
         %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 	% if BDD file does not exist, call ProbLog
 	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-	  trace,
+	  writeln(QueryID),
 	(
 	 recorded(QueryID, _, _)
 	->
@@ -635,13 +635,18 @@ init_one_query(QueryID,Query,Type) :-
 	  Query =.. [_,X,Y]
 	  ->
 	  Bdd = bdd(Dir, Tree, MapList),
-	  graph2bdd(X,Y,N,Bdd),
+	  (
+	      graph2bdd(X,Y,N,Bdd)
+	  ->
 	  rb_new(H0),
 	  maplist_to_hash(MapList, H0, Hash),
 	  Tree \= [],
-	  writeln(QueryID),
 	  tree_to_grad(Tree, Hash, [], Grad),
-	 recordz(QueryID,bdd(Dir, Grad, MapList),_)
+	  ;
+	  Bdd = bdd(-1,[],[]),
+	  Grad=[]
+	  ),
+	  recordz(QueryID,bdd(Dir, Grad, MapList),_)
 	 ;
 	  b_setval(problog_required_keep_ground_ids,false),
 	  rb_new(H0),
diff --git a/packages/yap-lbfgs/ex1.pl b/packages/yap-lbfgs/ex1.pl
index 77258b20d..fae5512c5 100644
--- a/packages/yap-lbfgs/ex1.pl
+++ b/packages/yap-lbfgs/ex1.pl
@@ -40,7 +40,6 @@ progress(FX,X,G,X_Norm,G_Norm,Step,_N,Iteration,Ls, 0) :-
 
 
 demo :-
-start_low_level_trace,
     format('Optimizing the function f(x0) = sin(x0)~n',[]),
 	optimizer_initialize(1,X,Status),
 
diff --git a/packages/yap-lbfgs/ex2.pl b/packages/yap-lbfgs/ex2.pl
index 1a6e0f30d..3a4f39320 100644
--- a/packages/yap-lbfgs/ex2.pl
+++ b/packages/yap-lbfgs/ex2.pl
@@ -44,7 +44,7 @@ progress(FX,X,_G,X_Norm,G_Norm,Step,_N,Iteration,Ls,0) :-
 
 demo :-
 	format('Optimizing the function f(x0,x1) = (x0-2)^2 + (x1-1)^2~n',[]),
-	optimizer_initialize(2,X),
+	optimizer_initialize(2,X,Status),
 
 
 	StartX0 is random*1000-500,
@@ -55,7 +55,7 @@ demo :-
 	X[1] <== StartX1,
 
 	
-	optimizer_run(BestF,Status),
+	optimizer_run(Status,BestF,BestX0, O),
 	BestX0 <== X[0],
 	BestX1 <== X[1],
 	
diff --git a/packages/yap-lbfgs/lbfgs.pl b/packages/yap-lbfgs/lbfgs.pl
index 14881398f..bec3cc7c7 100644
--- a/packages/yap-lbfgs/lbfgs.pl
+++ b/packages/yap-lbfgs/lbfgs.pl
@@ -162,18 +162,16 @@ optimizer_initialize(1)
 */
 
 optimizer_initialize(N,X,t(N,X,XO,Params)) :-
-	\+ initialized,
 
 	integer(N),
 	N>0,
 
 	% check whether there are such call back functions
 
-	optimizer_reserve_memory(N,X,XO,Params),
+	optimizer_reserve_memory(N,X,XO,Params).
 
 	% install call back predicates in the user module which call
 	% the predicates given by the arguments		
-	assert(initialized).
 
 /** @pred  optimizer_finalize/0
 Clean up the memory.