Per una descrizione del problema si veda l'articolo Intelligenza artificiale: un assaggio.
cifra(0). cifra(1). cifra(2). cifra(3). cifra(4). cifra(5). cifra(6). cifra(7). cifra(8). cifra(9). risolvi(A,B,C):- soluzione(A,B,C). soluzione(A,B,C) :- /* nessun riporto - solo D+S */ cifra(D), cifra(U), cifra(E), cifra(S), cifra(I), cifra(O), cifra(T), O is E + I, T is U + E, T is D + S - 10 + 1, O is 1, diversi(D,U,E,S,I,O,T), A is D*100+U*10+E, B is S*100+E*10+I, C is O*1000 + T*100 + T*10 +O, write(A), write(B), write(C). soluzione(A,B,C) :- /* riporto colonna unit e D+S*/ cifra(D), cifra(U), cifra(E), cifra(S), cifra(I), cifra(O), cifra(T), O is E + I - 10, T is U + E + 1, T is D + S - 10, O is 1, diversi(D,U,E,S,I,O,T), A is D*100+U*10+E, B is S*100+E*10+I, C is O*1000 + T*100 + T*10 + O, write(A), write(B), write(C). soluzione(A,B,C) :- /* riporto colonna decine e D+S */ cifra(D), cifra(U), cifra(E), cifra(S), cifra(I), cifra(O), cifra(T), O is E + I, T is U + E, T is D + S - 10, O is 1, diversi(D,U,E,S,I,O,T), A is D*100+U*10+E, B is S*100+E*10+I, C is O*1000 + T*100 + T*10 +O, write(A), write(B), write(C). soluzione(A,B,C) :- /* riporto colonne decine e unit e D+S */ cifra(D), cifra(U), cifra(E), cifra(S), cifra(I), cifra(O), cifra(T), O is E + I - 10, T is U + E + 1 - 10, T is D + S - 10 + 1, O is 1, diversi(D,U,E,S,I,O,T), A is D*100+U*10+E, B is S*100+E*10+I, C is O*1000 + T*100 + T*10 +O, write(A), write(B), write(C). diversi(D,U,E,S,I,O,T):- D == U, D == E, D == S, D == I, D == O, D == T, U == E, U == S, U == I, U == O, U == T, E == S, E == I, E == O, E == T, S == I, S == O, S == T, I == O, I == T, O == T.