Theorem Rnd_DN_UP_pt_N : forall F : R -> Prop, forall x d u f : R, F f -> Rnd_DN_pt F x d -> Rnd_UP_pt F x u -> (Rabs (f - x) <= x - d)%R -> (Rabs (f - x) <= u - x)%R -> Rnd_N_pt F x f.