MAYBE

Problem:
 minus(x,x) -> 0()
 minus(s(x),s(y)) -> minus(x,y)
 minus(0(),x) -> 0()
 minus(x,0()) -> x
 div(s(x),s(y)) -> s(div(minus(x,y),s(y)))
 div(0(),s(y)) -> 0()
 f(x,0(),b) -> x
 f(x,s(y),b) -> div(f(x,minus(s(y),s(0())),b),b)

Proof:
 Open