proposition: Lemma getfE V (f : {fmap K -> V}) (k : domf f) (kf : val k \in domf f) : f.[kf] = f k :> V.
proof: Proof. by congr (_ _); apply: val_inj. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)