The term {tt (mod $tau_1$ $tau_2$)} denotes the root of the object denoted by $tau_1$ modulo the object denoted by $tau_2$. The result will have the same sign as denoted by $tau_1$.
(= (Mod ?X 2) 0) (=> (Even-Integer ?X) (= (Mod ?X 2) 0)) (= (Mod ?X 2) 1) (=> (Odd-Integer ?X) (= (Mod ?X 2) 1))