proposition: Lemma big_ord_narrow : forall n1 n2 F, forall le_n1_n2 : n1 <= n2, let w := widen_ord le_n1_n2 in \big[op/idx]_(i < n2 | i < n1) F i === \big[op/idx]_(i < n1) F (w i).
proof: Proof. move=> *; exact: (big_ord_narrow_cond (predT)). Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq div choice fintype finfun paths Setoid Morphisms OperationClasses bigops