(VAR x y z )
(RULES 
        min(x, 0) -> 0
        min(0, y) -> 0
        min(s(x), s(y)) -> s(min(x, y))
        max(x, 0) -> x
        max(0, y) -> y
        max(s(x), s(y)) -> s(max(x, y))
        minus(x, 0) -> x
        minus(s(x), s(y)) -> s(minus(x, y))
        gcd(s(x), s(y)) -> gcd(minus(max(x, y), min(x, transform(y))), s(min(x, y)))
        transform(x) -> s(s(x))
        transform(cons(x, y)) -> cons(cons(x, x), x)
        transform(cons(x, y)) -> y
        transform(s(x)) -> s(s(transform(x)))
        cons(x, y) -> y
        cons(x, cons(y, s(z))) -> cons(y, x)
        cons(cons(x, z), s(y)) -> transform(x)
        
)