proposition: Lemma pi'_p'nat pi p n : pi^'.-nat n -> p \in pi -> p^'.-nat n.
proof: Proof. by move=> pi'n pi_p; apply: sub_in_pnat pi'n => q _; apply: contraNneq => ->. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(fintype div bigop)