Definition CoPrime (a b : nat) := gcd (Z_of_nat a) (Z_of_nat b) 1.

Lemma chRem1 :
forall b : nat,
b > 0 ->
forall a : Z,
{p : Z * nat | snd p < b /\ Z_of_nat (snd p) = (fst p * Z_of_nat b + a)%Z}.