proposition: Lemma big_ord_narrow_cond_leq n1 n2 (P : pred _) F (le_n12 : n1 <= n2) : let w := @widen_ord n1.+1 n2.+1 le_n12 in \big[op/idx]_(i < n2.+1 | P i && (i <= n1)) F i = \big[op/idx]_(i < n1.+1 | P (w i)) F (w i).
proof: Proof. exact: (@big_ord_narrow_cond n1.+1 n2.+1). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)