proposition: Lemma big_catl : forall r1 r2 (P : pred I) F, ~~ has P r2 -> \big[op/idx]_(i <- r1 ++ r2 | P i) F i === \big[op/idx]_(i <- r1 | P i) F i.
proof: Proof. by move=> r1 r2 P F; rewrite -> big_cat_nested; move/big_hasC=> Heq; rewrite -> Heq; reflexivity. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq div choice fintype finfun paths Setoid Morphisms OperationClasses bigops