MAYBE

Problem:
 cond(true(),x,y) -> cond(gr(x,y),x,add(x,y))
 gr(0(),x) -> false()
 gr(s(x),0()) -> true()
 gr(s(x),s(y)) -> gr(x,y)
 add(0(),x) -> x
 add(s(x),y) -> s(add(x,y))

Proof:
 Open