(VAR x y )
(RULES 
        not(true) -> false
        not(false) -> true
        odd(0) -> false
        odd(s(x)) -> not(odd(x))
        +(x, 0) -> x
        +(x, s(y)) -> s(+(x, y))
        +(s(x), y) -> s(+(x, y))
        
)