is_prime.pl

%****************************************************************************************************
%                                                                                                   *
%                                     Check if a Number is Prime                                    *
%                                                                                                   *
%       The given Prolog code defines a predicate `is_prime/1` to check if a number is prime.       *
%       The base cases define that numbers less than 2 are not prime. The recursive case checks     *
%       that the number N is not divisible by any number between 2 and sqrt(N).                     *
%                                                                                                   *
%                                       Example usage:                                              *
%                                      ?- is_prime(7).                                              *
%                                           true                                                    *
%                                                                                                   *
%****************************************************************************************************



% Base case: Numbers less than 2 are not prime.
is_prime(1) :- false.
is_prime(0) :- false.



% Recursive case: Check that the number N is not divisible by any number between 2 and sqrt(N).
is_prime(N) :-
    N > 1,
    \+ has_factor(N, 2).



% Check that the number N is divisible by F or any number between F and sqrt(N).
has_factor(N, F) :-
    F * F =< N,
    N mod F =:= 0.
has_factor(N, F) :-
    F * F =< N,
    F2 is F + 1,
    has_factor(N, F2).