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Generalizable All Variables.
Open Scope type_scope.
Section type_reification.
Inductive term :Type :=
Fun : term -> term -> term
| Prod : term -> term -> term
| Bool : term
| SET :term
| PROP :term
| TYPE :term
| Var : Type -> term.
Fixpoint interp (t:term) :=
match t with
Bool => bool
| SET => Set
| PROP => Prop
| TYPE => Type
| Fun a b => interp a -> interp b
| Prod a b => interp a * interp b
| Var x => x
end.
Class interp_pair (abs : Type) :=
{ repr : term;
link: abs = interp repr }.
Implicit Arguments repr [[interp_pair]].
Implicit Arguments link [[interp_pair]].
Lemma prod_interp `{interp_pair a, interp_pair b} : a * b = interp (Prod (repr a) (repr b)).
simpl. intros. rewrite <- link. rewrite <- (link b). reflexivity.
Qed.
Lemma fun_interp :forall `{interp_pair a, interp_pair b}, (a -> b) = interp (Fun (repr a) (repr b)).
simpl. intros. rewrite <- link. rewrite <- (link b). reflexivity.
Qed.
Coercion repr : interp_pair >-> term.
Definition abs `{interp_pair a} : Type := a.
Coercion abs : interp_pair >-> Sortclass.
Lemma fun_interp' :forall `{ia : interp_pair, ib : interp_pair}, (ia -> ib) = interp (Fun ia ib).
simpl. intros a ia b ib. rewrite <- link. rewrite <- (link b). reflexivity.
Qed.
Instance ProdCan `(interp_pair a, interp_pair b) : interp_pair (a * b) :=
{ repr := Prod (repr a) (repr b) ; link := prod_interp }.
Instance FunCan `(interp_pair a, interp_pair b) : interp_pair (a -> b) :=
{ link := fun_interp }.
Instance BoolCan : interp_pair bool :=
{ repr := Bool ; link := refl_equal _ }.
Instance VarCan x : interp_pair x | 10 := { repr := Var x ; link := refl_equal _ }.
Instance SetCan : interp_pair Set := { repr := SET ; link := refl_equal _ }.
Instance PropCan : interp_pair Prop := { repr := PROP ; link := refl_equal _ }.
Instance TypeCan : interp_pair Type := { repr := TYPE ; link := refl_equal _ }.
(* Print Canonical Projections. *)
Variable A:Type.
Variable Inhabited: term -> Prop.
Variable Inhabited_correct: forall `{interp_pair p}, Inhabited (repr p) -> p.
Lemma L : Prop * A -> bool * (Type -> Set) .
apply (Inhabited_correct _ _).
change (Inhabited (Fun (Prod PROP (Var A)) (Prod Bool (Fun TYPE SET)))).
Admitted.
End type_reification.
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