Im trying to get the following ?- count_nested([a,[1,2,[3]],[4,[5,[5],6]]],El). El = 8 With the following code count_nested([],0). count_nested([_|T],El):- count_nested(T,N), El is N + 1. But I get the following ?- count_nested([a,[1,2,[3]],[4,[5,[5],6]]],El). El = 3 Whats going on I just can't get ti to go throught the nested list?

hello, your code is counting thenumber of elements in the (most-outter) list. but i don't get what count_nested is supposed to do. if it should count the number of nested lists, then why it should return 8? if count_nest is supposed to counts all elements of the list which contains sublists as well, then you can just "flatten" the list by the (swi-prolog) builtin predicate "flatten". hope that then wtk =)

This code works too: cnt_nested([], 0). cnt_nested([H|T], N) :- list(H), !, cnt_nested(H, HN), cnt_nested(T, TN), N is HN + TN + 1. cnt_nested([_|T], N) :- cnt_nested(T, N). with the query you provided - cnt_nested([a,[1,2,[3]],[4,[5,[5],6]]],El). El -> 5. As WTK pointed out, why do u think it should return 8?? This code is independant of which Prolog u use too!

Appologies, list/1 is GNU prolog built-in. If your prolog doesn't have same (or similar) then use list([]). list([_|T]) :- list(T).