(* Shorthand for using a permutation to reindex a bigop. *)
Notation reindex_perm s := (reindex_inj (@perm_inj _ s)).

Lemma inj_tperm (T T' : finType) (f : T -> T') x y z : injective f -> f (tperm x y z) = tperm (f x) (f y) (f z).