assert (H := d_y).
assert (H0 := n_y).
reg.
Qed.
reg.
Qed.
reg.
Qed.
reg.
Qed.
reg.
Qed.
reg.
Qed.
reg.
Qed.
reg.
apply Rlt_0_1.
red; intro;  rewrite sqrt_1 in H; assert (H0 := R1_neq_R0); elim H0;
assumption.
Qed.

Lemma essai8 : derivable_pt (fun x : R => sqrt (Rsqr x + sin x + 1)) 0.