proposition: Lemma big_id_idem I (r : seq I) P F : op (\big[op/x]_(i <- r | P i) F i) x = \big[op/x]_(i <- r | P i) F i.
proof: Proof. by elim/big_rec : _ => // ? ? ?; rewrite -opA => ->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)