Check if all numbers in a list are different in prolog

Question

I want to create a rule in prolog that checks if there\'s a repeated number in a list.

For example:

• for [1,2,3,4] it will return tru

Answer 1

This isn't very efficient, but for each number you can check if it appears again later. Like so:

Different([H|T]):-
  CheckSingle(H, [T]),
  Different([T]).

Checksingle(_,[]).

Checksingle(Elem, [H, T]):-
  Elem != H,
  Checksingle(Elem, [T]).