proposition: Lemma fgraphK : cancel fgraph Finfun.
proof: Proof. by move=> f; apply/ffunP=> x; rewrite ffunE tnth_fgraph enum_rankK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype tuple)