intros; unfold dydt, dy in |- *; ring.
Qed.

(* Specifications: *)
(**********)
Lemma R_equal_when_zero :
forall (intruder evader : State) (t1 t2 : R),
div_tau intruder evader = 0%R ->
RR intruder evader t1 = RR intruder evader t2.