Instance Fin_eq_dec n : eq_dec (Fin.t n).
(* (** * finTypes from Lists  *) *)
(* (* Conversion of lists over eqTypes to finite types *) *)
(* (* *) *)
(** * Pure predicates  *)
(* taken from the development of Herditarily finite sets by Prof. Smolka and Kathrin Stark. *)
(* *)
Definition pure (X:Type) (p: X -> Prop) {D:forall x, dec (p x)} x := if Dec (p x) then True else False.
Arguments pure {X} p {D} x.

Lemma pure_impure  (P: Prop) (_: dec P) (norm: if Dec (P) then True else False) : P.