assert (H := d_y).
assert (H0 := n_y).
reg.
Qed.
reg.
Qed.
reg.
Qed.
reg.
Qed.
reg.
Qed.
reg.
Qed.
reg.
Qed.

Lemma essai7 :
derivable_pt (fun x : R => (cos (/ sqrt x) * Rsqr (sin x + 1))%R) 1.