Proof with trivial.
unfold distance, d in |- *; unfold Die in |- *; simpl in |- *;
unfold xi, yi in |- *...
Qed.

Lemma R_T :
forall (intr : Trajectory) (evad : EvaderTrajectory) (T : TimeT),
h (tr evad) = V ->
Rsqr (RR (measure2state intr 0) (measure2state (tr evad) 0) T) =
(Rsqr (l intr evad T * cos (beta intr evad T + thetat intr 0) - V * T) +
Rsqr (l intr evad T * sin (beta intr evad T + thetat intr 0)))%R.