assumption.
elim H; intro.
generalize (Rsqr_DRs 0); intro H1; rewrite <- H0 in H1; rewrite Rs_0 in H1;
repeat rewrite Rsqr_0 in H1; rewrite Rplus_0_l in H1;
rewrite Rmult_0_l in H1; generalize (eq_sym 0 (Rsqr (vi intr)) H1).
clear H1; intro H1; generalize (Rsqr_eq_0 (vi intr) H1).
intro H2; generalize (TypeSpeed_pos (vi intr)); intro H3; rewrite H2 in H3;
elim (Rlt_irrefl 0 H3).
generalize D_Rs_0; intro H1;
elim
(Rlt_irrefl 0 (Rle_lt_trans 0 (derive_pt Rs 0 (Rs_derivable 0%R)) 0 H1 H0)).
Qed.

(**********)
Lemma D_alphas_0 :
(2 * derive_pt alphas 0 (cond_D1 alphas 0))%R =
derive_pt thetat 0 (thetat_derivable 0%R).