(** We now define lcm thanks to gcd:  lcm a b = a * (b / gcd a b) = (a / gcd a b) * b = (a*b) / gcd a b  Nota: [lcm 0 0] should be 0, which isn't guarantee with the third equation above. *)
#[global]
Instance lcm_wd : Proper (eq==>eq==>eq) lcm.

Lemma lcm_mul_mono_r :
forall n m p, lcm (n * p) (m * p) == lcm n m * p.