MAYBE

Problem:
 minus(x,y) -> cond(min(x,y),x,y)
 cond(y,x,y) -> s(minus(x,s(y)))
 min(0(),v) -> 0()
 min(u,0()) -> 0()
 min(s(u),s(v)) -> s(min(u,v))

Proof:
 Open