(VAR x y z )
(RULES 
        minus(x, 0) -> x
        minus(s(x), s(y)) -> minus(x, y)
        double(0) -> 0
        double(s(x)) -> s(s(double(x)))
        plus(0, y) -> y
        plus(s(x), y) -> s(plus(x, y))
        plus(s(x), y) -> plus(x, s(y))
        plus(s(x), y) -> s(plus(minus(x, y), double(y)))
        plus(s(plus(x, y)), z) -> s(plus(plus(x, y), z))
        
)