(VAR b1 b2 x y )
(RULES 
        le(0, y) -> true
        le(s(x), 0) -> false
        le(s(x), s(y)) -> le(x, y)
        zero(0) -> true
        zero(s(x)) -> false
        id(0) -> 0
        id(s(x)) -> s(id(x))
        minus(x, 0) -> x
        minus(s(x), s(y)) -> minus(x, y)
        mod(x, y) -> if_mod(zero(x), zero(y), le(y, x), id(x), id(y))
        if_mod(true, b1, b2, x, y) -> 0
        if_mod(false, b1, b2, x, y) -> if2(b1, b2, x, y)
        if2(true, b2, x, y) -> 0
        if2(false, b2, x, y) -> if3(b2, x, y)
        if3(true, x, y) -> mod(minus(x, y), s(y))
        if3(false, x, y) -> x
        
)