proposition: Lemma exchange_big_nat_idem m1 n1 m2 n2 (P Q : pred nat) F : \big[op/x]_(m1 <= i < n1 | P i) \big[op/x]_(m2 <= j < n2 | Q j) F i j = \big[op/x]_(m2 <= j < n2 | Q j) \big[op/x]_(m1 <= i < n1 | P i) F i j.
proof: Proof. rewrite (exchange_big_dep_nat_idem Q) //. by under eq_bigr => i Qi do under eq_bigl do rewrite Qi andbT. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)