Does an element exists in a list of lists?

Question

I want to find if a given element exists in a list of lists. I am only getting true if the element exists somewhere is the first list of lists.

Any advice?

memberlist(X,[[X|T1]|T2]).
memberlist(X,[[H|T1]|T2]) :-
  memberlist(X,[T1|T2]).

Answer 1

Here is my approach using sort/2 and flat/2 that flatten a list only one level:

memberlists(X, Xss) :- Xss = [_|_], 
                       flat(Xss, FL), 
                       sort(FL, OutL), 
                       memberd(X, OutL).

memberd(X, [X|_Xs]).
memberd(X, [Y|Xs]) :-
   dif(X,Y),
   memberd(X, Xs).                       

flat([],[]).
flat([H|T],R) :- H = [_|_], flat(T,T1), append(H,T1,R).

Testcases:

 ?- memberlists(X,[[a,A]]), A = a.
X = A, A = a ;
false.

?- memberlists(X,[[a]|Xs]), Xs = [_|_].
Xs = [[X]] ;
X = a,
Xs = [[_G13004]],
dif(a, _G13004) ;
Xs = [[X, _G12784]] .

?- memberlists(X,[[a,a],[Y],[b]]).
X = Y ;
X = a,
dif(a, Y) ;
X = b,
dif(b, Y) ;
false.

?- memberlists(X,[[a,a],[a],[a]]).
X = a ;
false.

?- memberlists(X,[[[a,a],[a],[a]]]).
X = [a] ;
X = [a, a] ;
false.

?- memberlists(X,[L]).
L = [X] ;
L = [X, _G12710] ;
L = [_G12923, X],
dif(X, _G12923) ;
L = [X, _G12710, _G12716] ;
L = [_G12935, X, _G12941],
dif(X, _G12935) . (and goes on...)

?- memberlists(X,L).
L = [[X]]
L = [[X, _G12704]] ;
L = [[_G12920, X]],
dif(X, _G12920) ;
L = [[X, _G12704, _G12710]] ;
L = [[_G12932, X, _G12938]],
dif(X, _G12932) ;
L = [[_G13018, _G13021, X]],
dif(X, _G13021),
dif(X, _G13018) ;
L = [[X, _G12704, _G12710, _G12716]] . (and goes on...)