Require Export misc.
Require Export Zstruct.
Require Export ZArith.
Unset Standard Proposition Elimination Names.

Lemma gcd_unicity_apart_sign :
forall a b c d : Z,
is_gcd Z IdZ Zmult 0%Z a b c ->
is_gcd Z IdZ Zmult 0%Z a b d -> d = c \/ d = (- c)%Z.