proposition: Lemma big_tuple I n (t : n.-tuple I) (P : pred I) F : \big[op/idx]_(i <- t | P i) F i = \big[op/idx]_(i < n | P (tnth t i)) F (tnth t i).
proof: Proof. by rewrite big_tnth tvalK; case: _ / (esym _). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)