Notation Zgcd_inv_0_l := Z.gcd_eq_0_l (only parsing).
Notation Zgcd_inv_0_r := Z.gcd_eq_0_r (only parsing).

Lemma Zgcd_ass a b c : Z.gcd (Z.gcd a b) c = Z.gcd a (Z.gcd b c).
Notation Zgcd_Zabs := Z.gcd_abs_l (only parsing).