Problem:
 f(u(O()),u(y)) -> A()
 f(v(x),v(O())) -> B()
 O() -> u(O())
 O() -> v(O())
 u(x) -> x
 v(x) -> x
 f(x,y) -> f(x,u(y))
 f(x,y) -> f(v(x),y)

Proof:
 Open