divisible(X, Y) :-
  0 is X mod Y, !.

divisible(X, Y) :-
  X > Y + 1,
  divisible(X, Y + 1).

prime(2) :-
  true, !.

prime(X) :-
  X < 2, !, false.

prime(X) :-
  not(divisible(X, 2)).

% =============================================================

main :-
  143 = prime(P) * 13,
  writef('%t\n', [P]).