MAYBE

Problem:
 -(x,0()) -> x
 -(s(x),s(y)) -> -(x,y)
 +(0(),y) -> y
 +(s(x),y) -> s(+(x,y))
 *(x,0()) -> 0()
 *(x,s(y)) -> +(x,*(x,y))
 f(s(x)) -> f(-(+(*(s(x),s(x)),*(s(x),s(s(s(0()))))),*(s(s(x)),s(s(x)))))

Proof:
 Open