proposition: Lemma big_ord_narrow_leq : forall n1 n2 F, forall le_n1_n2 : n1 <= n2, let w := @widen_ord n1.+1 n2.+1 le_n1_n2 in \big[op/idx]_(i < n2.+1 | i <= n1) F i === \big[op/idx]_(i < n1.+1) F (w i).
proof: Proof. move=> *; exact: (big_ord_narrow_cond_leq (predT)). Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq div choice fintype finfun paths Setoid Morphisms OperationClasses bigops