(VAR x y )
(RULES 
        times(x, 0) -> 0
        times(x, s(y)) -> plus(times(x, y), x)
        plus(x, 0) -> x
        plus(0, x) -> x
        plus(x, s(y)) -> s(plus(x, y))
        plus(s(x), y) -> s(plus(x, y))
        
)