(VAR c x y )
(RULES 
        le(0, y) -> true
        le(s(x), 0) -> false
        le(s(x), s(y)) -> le(x, y)
        minus(x, 0) -> x
        minus(0, s(y)) -> 0
        minus(s(x), s(y)) -> minus(x, y)
        plus(x, 0) -> x
        plus(x, s(y)) -> s(plus(x, y))
        mod(s(x), 0) -> 0
        mod(x, s(y)) -> help(x, s(y), 0)
        help(x, s(y), c) -> if(le(c, x), x, s(y), c)
        if(true, x, s(y), c) -> help(x, s(y), plus(c, s(y)))
        if(false, x, s(y), c) -> minus(x, minus(c, s(y)))
        
)