(**********)
Definition Rsqr_Rmin (intruder evader : State) : R :=
  match Req_EM_var (Ax2_R intruder) 0 with
  | left _ => 0%R
  | right _ =>
      ((4 * Ax2_R intruder * C_R intruder evader -
        Rsqr (Bx_R intruder evader)) / (4 * Ax2_R intruder))%R
  end.

Lemma tmin_0 : forall intruder evader : State, div_tau intruder evader <> 0%R -> tmin intruder evader = (- Bx_R intruder evader / (2 * Ax2_R intruder))%R.