Notation Zgcd_0 := Z.gcd_0_r (only parsing).
Notation Zgcd_1 := Z.gcd_1_r (only parsing).
#[global]
Hint Resolve Z.gcd_0_r Z.gcd_1_r : zarith.

Theorem Zgcd_1_rel_prime : forall a b,
Z.gcd a b = 1 <-> rel_prime a b.