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(* as published by the Free Software Foundation; either version 2.1   *)
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(* GNU General Public License for more details.                       *)
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(* 02110-1301 USA                                                     *)
(** Relative primality *)
Definition rel_prime (a b : Z) : Prop := gcd a b 1.
(** Bezout's theorem: [a] and [b] are relatively prime if and only if there exist [u] and [v] such that [ua+vb = 1]. *)
(** Gauss's theorem: if [a] divides [bc] and if [a] and [b] are relatively prime, then [a] divides [c]. *)
(** If [a] is relatively prime to [b] and [c], then it is to [bc] *)

Lemma rel_prime_mult :
forall a b c : Z, rel_prime a b -> rel_prime a c -> rel_prime a (b * c).