--- /dev/null
+(*********************************************************************************************************************************)
+(* ProgrammingLanguageFlattening *)
+(*********************************************************************************************************************************)
+
+Generalizable All Variables.
+Require Import Preamble.
+Require Import General.
+Require Import Categories_ch1_3.
+Require Import InitialTerminal_ch2_2.
+Require Import Functors_ch1_4.
+Require Import Isomorphisms_ch1_5.
+Require Import ProductCategories_ch1_6_1.
+Require Import OppositeCategories_ch1_6_2.
+Require Import Enrichment_ch2_8.
+Require Import Subcategories_ch7_1.
+Require Import NaturalTransformations_ch7_4.
+Require Import NaturalIsomorphisms_ch7_5.
+Require Import MonoidalCategories_ch7_8.
+Require Import Coherence_ch7_8.
+Require Import Enrichment_ch2_8.
+Require Import RepresentableStructure_ch7_2.
+Require Import FunctorCategories_ch7_7.
+
+Require Import Reification.
+Require Import NaturalDeduction.
+Require Import NaturalDeductionCategory.
+Require Import ProgrammingLanguage.
+Require Import ProgrammingReification.
+
+Section Flattening.
+
+ Context (Guest:ProgrammingLanguageSMME) (Host :ProgrammingLanguageSMME).
+ Context (GuestHost:TwoLevelLanguage).
+
+ Definition FlatObject (x:TypesL _ _ Host) :=
+ forall y1 y2, not ((reification_r_obj GuestHost y1 y2)=x).
+
+ Definition FlatSubCategory := FullSubcategory (TypesL _ _ Host) FlatObject.
+
+ Context (F:Retraction (TypesL _ _ Host) FlatSubCategory).
+
+ Definition FlatteningOfReification :=
+ garrow_from_reification Guest Host GuestHost >>>> F.
+
+ Lemma FlatteningIsNotDestructive :
+ FlatteningOfReification >>>> retraction_retraction F >>>> HomFunctor _ (me_i Host) ≃ GuestHost.
+ apply if_inv.
+ set (@roundtrip_reification_to_reification _ Guest _ _ Host GuestHost) as q.
+ unfold mf_f in *; simpl in *.
+ apply (if_comp q).
+ clear q.
+ unfold me_mf; simpl.
+ unfold mf_f; simpl.
+ refine (if_respects _ (if_id _)).
+ unfold FlatteningOfReification.
+ unfold mf_f; simpl.
+ eapply if_comp.
+ Focus 2.
+ eapply if_inv.
+ apply (if_associativity (garrow_functor Guest Host GuestHost) F (retraction_retraction F)).
+ eapply if_comp.
+ eapply if_inv.
+ apply if_right_identity.
+ refine (if_respects (if_id _) _).
+ apply if_inv.
+ apply retraction_composes.
+ Qed.
+
+End Flattening.
+
+