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