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

Lemma theta_inv : forall t : R, (0 <= t)%R -> (thetat intr 0 - rho_vi * t <= thetat intr t)%R /\ (thetat intr t <= thetat intr 0 + rho_vi * t)%R.