by move/ltnW->.
rewrite leq_eqVlt; case/orP; first by move/eqP->.
by move/modp_small; rewrite rpq => h; move: nq0; rewrite h eqxx.
Qed.

Lemma eqp_eq p q: p %= q -> (lead_coef q) *: p = (lead_coef p) *: q.