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

Lemma Dyp : forall t : R, derive_pt yp t (yp_derivable t) = (v (vi intr) * sin (thetat intr t - thetat intr 0))%R.