proposition: Lemma val_in_fset A (p : finmempred _) (k : A) : (val k \in imfset key val p) = (in_mem k p).
proof: Proof. by rewrite mem_imfset ?in_finmempred //; exact: val_inj. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)