Prolog is also like this: ?- x is -4 mod 2. X = 0. ?- X is -8 mod 2. X = 0. ?- X is -9 mod 2. X = 1. Using declarative integer arithm

Prolog is also like this: ?- x is -4 mod 2. X = 0. ?- X is -8 mod 2. X = 0. ?- X is -9 mod 2. X = 1. Using declarative integer arithmetic, we can even express very generally that a number X is a multiple of 2: ?- X #= 2*_. This is true iff there is any integer (indicated by an anonymous variable _) that, multiplied by 2, yields X. It works for positive and negative integers. For example: ?- -4 #= 2*_. true. ?- -9 #= 2*_. false. A very nice reference on the general topic of bitwise operations is Donald Knuth's Bitwise Tricks and Techniques in Volume 4 of The Art of Computer Programming.