Definition R_p4 (x y : Z) :=
  0 <= x /\ 1 < y /\ exists d : Z, y = d * d * x /\ 1 < d.

Lemma sqr_prime2 : forall a b c : Z, (a | b) -> (a * a | b * c) -> prime a -> (a * a | b) \/ (a | c).