(VAR x y )
(STRATEGY INNERMOST)
(RULES 
        -(x,0) -> x
        -(s(x),s(y)) -> -(x,y)
        p(s(x)) -> x
        f(s(x),y) -> f(p(-(s(x),y)),p(-(y,s(x))))
        f(x,s(y)) -> f(p(-(x,s(y))),p(-(s(y),x)))
        
)