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Inductive divides : nat -> nat -> Prop :=
    dividesDef : forall a b q : nat, b = q * a -> divides a b.(******************************************************************************)
 
Inductive divides : nat -> nat -> Prop :=
    dividesDef : forall a b q : nat, b = q * a -> divides a b.

Lemma divides_dec' : forall x y : nat, {(exists q : _, is_div x y q 0)} + {~ (exists q : _, is_div x y q 0)}.