Programming 08/ 11/ 2016

/* Prolog is easy */

/* Determinate if number is prime */
prost(N):- N >= 2, prost(N, 2).
prost(N, A):- A < (N div 2) + 1, (N mod A) =\= 0, A1 is A + 1, prost(N, A1).
prost(N, A):- A >= (N div 2) + 1.

/* Write all prime numbers from 1 to N */
primes(N, A):- N > 0, prost(N), A is N.
primes(N, A):- N > 0, N1 is N - 1, primes(N1, A).

/* The biggest digit of the number N */
max(A, B, A):- A >= B.
max(A, B, B):- A < B.
maxdigit(N, A):- N > 0, X is N mod 10, N1 is N div 10,
    maxdigit(N1, A1), max(A1, X, A).
maxdigit(0, 0).