/*

    MAC/MCSs/MRes - 2015-16
    Module 534: Intro to Prolog

    File: sample.pl  -  nr600

*/

check_integer( 0 ).
/*check_integer( 1 ).*/
check_integer( N ) :-
    N > 0,
    N1 is N - 2,
    check_integer( N1 ).
check_integer( N ) :-
    N < 0,
    N1 is N + 2,
    check_integer( N1 ).