(VAR x y )
(STRATEGY INNERMOST)
(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))
        -(x,0) -> x
        -(s(x),s(y)) -> -(x,y)
        gcd(s(x),0) -> s(x)
        gcd(0,s(x)) -> s(x)
        gcd(s(x),s(y)) -> gcd(-(max(x,y),min(x,y)),s(min(x,y)))
        
)