:- dynamic(app/3).
:- initialization(gui_trace_call_predicate(app/3)).

app([],B,B).
app([X|A],B,[X|C]):- app(A,B,C).

:- dynamic(mem/2).
:- initialization(gui_trace_call_predicate(mem/2)).

mem(X,[X|_]).
mem(X,[_|L]):- mem(X,L).