gistfile1.pl

fact(0, 1).
fact(N, F) :-
  N > 0,
  N1 is N-1,
  fact(N1, F1),
  F is N*F1.

fib(0, 0).
fib(1, 1).
fib(N, F) :-
  N > 1,
  N1 is N-1, fib(N1, F1),
  N2 is N-2, fib(N2, F2),
  F is F1 + F2.

collatz(1).
collatz(N) :-
  N > 1, N mod 2 =:= 0,
  N1 is N//2,
  write(N1), write(' '),
  collatz(N1).
collatz(N) :-
  N > 1, N mod 2 =:= 1,
  N1 is 3*N+1,
  write(N1), write(' '),
  collatz(N1).

inS(0).
inS(N) :-
  N > 0, (N-1) mod 2 =:= 0,
  N1 is (N-1)//2, inS(N1).
inS(N) :-
  N > 0, (N-1) mod 3 =:= 0,
  N1 is (N-1)//3, inS(N1).

hanoi(0, _, _, _).
hanoi(N, X, Y, Z) :-
  N > 0, N1 is N-1,
  hanoi(N1, X, Z, Y),
  write('move '), write(N),
  write(' from '), write(X),
  write(' to '), write(Y), nl,
  hanoi(N1, Z, Y, X).

factsum(1, 1).
factsum(N, S) :-
  N > 1, N1 is N-1,
  fact(N, S1),
  factsum(N1, S2),
  S is S1+S2.

gcd(0, B, B).
gcd(A, B, G) :-
  A > 0,
  R is B mod A,
  gcd(R, A, G).