(* We can't declare a canonical structure here because we've already *)
(* stated that subType_sort and FinType.sort unify via to the        *)
(* subType_finType structure.                                        *)
Definition SubFinMixin_for (eT : eqType) of phant eT :=
eq_rect _ Finite.mixin_of SubFinMixin eT.
Variable sfT : subFinType P.

Lemma card_sub : #|sfT| = #|[pred x | P x]|.
Definition seq_sub_pickle x := index x seq_sub_enum.