proposition: Lemma morphpreP : reflect (x \in D /\ f x \in R) (x \in D :&: f @^-1: R).
proof: Proof. by rewrite !inE; apply: andP. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup)