Definition e (t : R) : R := sqrt (Rsqr_evader_distance t).Definition i (t : R) : R := sqrt (Rsqr_intruder_distance t).

Lemma Dyp0_PI2 : forall t : R, (0 <= t)%R -> (rho_vi * t <= PI / 2)%R -> (- (vi intr * sin (rho_vi * t)) <= derive_pt yp t (yp_derivable t) <= vi intr * sin (rho_vi * t))%R.