intros; apply Rplus_le_compat.
apply Rle_trans with (l1 * sin a)%R.
apply Rmult_le_compat_l.
assumption.
generalize (SIN a H (Rlt_le a PI (Rle_lt_trans a (PI / 2) PI H0 PI2_Rlt_PI)));
intro; elim H3; intros; assumption.
apply Rmult_le_compat_r.
apply (sin_ge_0 a H (Rlt_le a PI (Rle_lt_trans a (PI / 2) PI H0 PI2_Rlt_PI))).
assumption.
rewrite <- (Ropp_involutive (r_ub V * (cos_lb (rho_ub V * MaxT) - 1)));
rewrite <- (Ropp_involutive (r_V * (cos (rho_V * T) - 1)));
apply Ropp_ge_le_contravar; apply Rle_ge;
replace (- (r_V * (cos (rho_V * T) - 1)))%R with
(r_V * (1 - cos (rho_V * T)))%R.
replace (- (r_ub V * (cos_lb (rho_ub V * MaxT) - 1)))%R with
(r_ub V * (1 - cos_lb (rho_ub V * MaxT)))%R.
apply Rmult_le_compat.
left; apply r_V_is_pos.
apply Rplus_le_reg_l with (cos (rho_V * T)); rewrite Rplus_0_r;
rewrite Rplus_comm; unfold Rminus in |- *; repeat rewrite Rplus_assoc;
rewrite Rplus_opp_l; rewrite Rplus_0_r; generalize (COS_bound (rho_V * T));
intro; elim H3; intros; assumption.
unfold r_V in |- *; left; apply r_ub_0.
apply Rplus_le_reg_l with (Ropp 1); unfold Rminus in |- *;
repeat rewrite <- Rplus_assoc; repeat rewrite Rplus_opp_l;
repeat rewrite Rplus_0_l; apply Ropp_ge_le_contravar;
apply Rle_ge; apply Rle_trans with (cos (rho_ub V * MaxT)).
cut (- PI / 2 <= rho_ub V * MaxT <= PI / 2)%R.
intro; elim H3; intros; generalize (COS (rho_ub V * MaxT) H4 H5); intro;
elim H6; intros; assumption.
split.
left; apply Rlt_le_trans with 0%R.
replace (- PI / 2)%R with (- (PI / 2))%R.
apply _PI2_RLT_0.
unfold Rdiv in |- *; symmetry  in |- *; apply Ropp_mult_distr_l_reverse.
apply Rmult_le_pos.
left; apply rho_ub_pos.
left; unfold MaxT in |- *.
prove_sup.
cut (MaxT <= MaxT)%R.
intro; left; apply (rho_ub_t_PI2 V (mkTimeT MaxT MinT_MaxT H3)).
right; reflexivity.
apply cos_decr_1.
left; apply Rmult_lt_0_compat.
apply rho_V_is_pos.
apply Rlt_le_trans with MinT.
apply MinT_is_pos.
apply (cond_1 T).
left; apply Rlt_trans with (PI / 2)%R.
apply (rho_t_PI2 T).
apply PI2_Rlt_PI.
left; apply Rmult_lt_0_compat.
apply rho_ub_pos.
unfold MaxT in |- *; prove_sup.
left; apply Rlt_trans with (PI / 2)%R.
cut (MaxT <= MaxT)%R.
intro; apply (rho_ub_t_PI2 V (mkTimeT MaxT MinT_MaxT H3)).
right; reflexivity.
apply PI2_Rlt_PI.
apply Rmult_le_compat.
left; apply rho_V_is_pos.
left; apply Rlt_le_trans with MinT; [ apply MinT_is_pos | apply (cond_1 T) ].
left; unfold rho_V in |- *; apply rho_ub_0.
apply (cond_2 T).
ring.
ring.
Qed.

(**********)
Lemma Math_prop_x_a_PI2 :
forall (a l : R) (T : TimeT),
(MinBeta <= a)%R ->
(a <= PI / 2)%R ->
(0 <= l)%R ->
(r_V * sin (rho_V * T) - l * cos MinBeta <=
r_V * sin (rho_V * T) - l * cos a)%R.