MAYBE

Problem:
 minus(x,y) -> cond(gt(x,y),x,y)
 cond(false(),x,y) -> 0()
 cond(true(),x,y) -> s(minus(x,s(y)))
 gt(0(),v) -> false()
 gt(s(u),0()) -> true()
 gt(s(u),s(v)) -> gt(u,v)

Proof:
 Open