Intersection and union of 2 lists

Question

i\'m starting up learning prolog (i use SWI-prolog) and i did a simple exercise in which i have 2 lists and i want to calculate their intersection and union. Here is my code

Answer 1

% Element X is in list?

pert(X, [ X | _ ]).

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

% Union of two list

union([ ], L, L).

union([ X | L1 ], L2, [ X | L3 ]):- \+pert(X, L2), union(L1, L2, L3).

union([ _ | L1 ], L2, L3):- union(L1, L2, L3).

% Intersection of two list

inter([ ], _, [ ]).

inter([ X | L1 ], L2, [ X | L3 ]):- pert(X, L2), inter(L1, L2, L3).

inter([ _ | L1 ], L2, L3):- inter(L1, L2, L3).