case (total_order_T (cos (alphas x)) 0); intro.
elim s; intro.
cut (cos (alphas x) <> 0%R).
intro;
cut
(exists eps : posreal,
(forall h : R, (Rabs h < eps)%R -> cos (alphas (x + h)%R) <> 0%R)).
set (xi_p := fun t : R => xi intr t).
intro;
cut (derivable_pt (fun t : R => ((xi_p t - xi_p 0) / cos (alphas t))%R) x).
intro X; unfold derivable_pt in X; elim X; intros l H1.
unfold derivable_pt in |- *; exists l.
unfold derivable_pt_abs in H1; unfold derivable_pt_lim in H1;
unfold derivable_pt_abs in |- *; unfold derivable_pt_lim in |- *;
intros.
elim (H1 eps H2); intros del H3.
elim H0; intros dom H4.
cut (0 < Rmin del dom)%R.
intro; exists (mkposreal (Rmin del dom) H5); intros.
repeat rewrite Rs_x.
unfold xi_p in H3; apply H3.
assumption.
apply Rlt_le_trans with (Rmin del dom); [ apply H7 | apply Rmin_l ].
apply H.
apply H4; apply Rlt_le_trans with (Rmin del dom); [ apply H7 | apply Rmin_r ].
unfold Rmin in |- *; case (Rle_dec del dom); intro.
apply (cond_pos del).
apply (cond_pos dom).
set (alphas_p := d2 alphas); reg.
unfold alphas_p in |- *; apply (cond_D1 alphas).
apply (xi_derivable intr x).
set (alphas_p := d2 alphas); set (f := fun t : R => cos (alphas_p t)).
cut
(exists eps : posreal,
(forall h : R, (Rabs h < eps)%R -> f (x + h)%R <> 0%R)).
intro; elim H0; intros.
exists x0; intros; unfold f in H1; apply H1; assumption.
apply continuous_neq_0.
unfold f in |- *; reg; apply derivable_continuous_pt; apply (cond_D1 alphas).
apply H.
red in |- *; intro; rewrite H in a; elim (Rlt_irrefl _ a).
cut (sin (alphas x) <> 0%R).
intro;
cut
(exists eps : posreal,
(forall h : R, (Rabs h < eps)%R -> sin (alphas (x + h)%R) <> 0%R)).
set (yi_p := fun t : R => yi intr t).
intro;
cut (derivable_pt (fun t : R => ((yi_p t - yi_p 0) / sin (alphas t))%R) x).
intro X; unfold derivable_pt in X.
elim X; intros l H1.
unfold derivable_pt in |- *; exists l.
unfold derivable_pt_abs in H1; unfold derivable_pt_lim in H1;
unfold derivable_pt_abs in |- *; unfold derivable_pt_lim in |- *;
intros.
elim (H1 eps H2); intros del H3.
elim H0; intros dom H4.
cut (0 < Rmin del dom)%R.
intro; exists (mkposreal (Rmin del dom) H5); intros.
repeat rewrite Rs_y.
unfold yi_p in H3; apply H3.
assumption.
apply Rlt_le_trans with (Rmin del dom); [ apply H7 | apply Rmin_l ].
apply H.
apply H4; apply Rlt_le_trans with (Rmin del dom); [ apply H7 | apply Rmin_r ].
unfold Rmin in |- *; case (Rle_dec del dom); intro.
apply (cond_pos del).
apply (cond_pos dom).
set (alphas_p := d2 alphas); reg.
unfold alphas_p in |- *; apply (cond_D1 alphas).
apply (yi_derivable intr x).
set (alphas_p := d2 alphas); set (f := fun t : R => sin (alphas_p t)).
cut
(exists eps : posreal,
(forall h : R, (Rabs h < eps)%R -> f (x + h)%R <> 0%R)).
intro; elim H0; intros.
exists x0; intros; unfold f in H1; apply H1; assumption.
apply continuous_neq_0.
unfold f in |- *; reg; apply derivable_continuous_pt; apply (cond_D1 alphas).
apply H.
assert (H := cos_sin_0_var (alphas x)); elim H; intro.
elim H0; assumption.
exact H0.
cut (cos (alphas x) <> 0%R).
intro;
cut
(exists eps : posreal,
(forall h : R, (Rabs h < eps)%R -> cos (alphas (x + h)%R) <> 0%R)).
set (xi_p := fun t : R => xi intr t).
intro;
cut (derivable_pt (fun t : R => ((xi_p t - xi_p 0) / cos (alphas t))%R) x).
intro X; unfold derivable_pt in X; elim X; intros l H1.
unfold derivable_pt in |- *; exists l.
unfold derivable_pt_abs in H1; unfold derivable_pt_lim in H1;
unfold derivable_pt_abs in |- *; unfold derivable_pt_lim in |- *;
intros.
elim (H1 eps H2); intros del H3.
elim H0; intros dom H4.
cut (0 < Rmin del dom)%R.
intro; exists (mkposreal (Rmin del dom) H5); intros.
repeat rewrite Rs_x.
unfold xi_p in H3; apply H3.
assumption.
apply Rlt_le_trans with (Rmin del dom); [ apply H7 | apply Rmin_l ].
apply H.
apply H4; apply Rlt_le_trans with (Rmin del dom); [ apply H7 | apply Rmin_r ].
unfold Rmin in |- *; case (Rle_dec del dom); intro.
apply (cond_pos del).
apply (cond_pos dom).
set (alphas_p := d2 alphas); reg.
unfold alphas_p in |- *; apply (cond_D1 alphas).
apply (xi_derivable intr x).
set (alphas_p := d2 alphas); set (f := fun t : R => cos (alphas_p t)).
cut
(exists eps : posreal,
(forall h : R, (Rabs h < eps)%R -> f (x + h)%R <> 0%R)).
intro; elim H0; intros.
exists x0; intros; unfold f in H1; apply H1; assumption.
apply continuous_neq_0.
unfold f in |- *; reg; apply derivable_continuous_pt; apply (cond_D1 alphas).
apply H.
red in |- *; intro; rewrite H in r; elim (Rlt_irrefl _ r).
Qed.
Definition alphas_p : R -> R := d2 alphas.

Lemma fct_der4 :
forall t : R,
derivable_pt ((Rs * comp cos alphas_p)%F + fct_cte (xi intr 0)) t.