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(*                                                                    *)
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(* 02110-1301 USA                                                     *)
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(*          Projet Formel - Calculus of Inductive Constructions V5.10        *)
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(*									     *)
(*            2nd definition (Equational) of Adjunctions       		     *)
(*									     *)
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(*									     *)
(*                     A. SAIBI	  May 95                  		     *)
(*									     *)
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Require Export IdCAT.
Require Export Adj_UA.
Set Implicit Arguments.
Unset Strict Implicit.
(* lois des NT: eta et epsilon *)
Section adj1_def.
Variables (C D : Category) (F : Functor D C) (G : Functor C D).
Section adj1_laws.
Variables (eta : NT (Id_CAT D) (F o_F G)) (eps : NT (G o_F F) (Id_CAT C)).
(* Rmq: on utilise idCAT, qui de'finit Id_CAT sans parler de Functor_Setoid. Evitant ainsi l'inconsistance des univers *)
Definition Adj1_law1 :=
forall c : C, eta (G c) o FMor G (eps c) =_S Id (G c).
Definition Adj1_law2 :=
forall d : D, FMor F (eta d) o eps (F d) =_S Id (F d).
End adj1_laws.
Structure Adj1 : Type :=
{A_eta : NT (Id_CAT D) (F o_F G);
A_eps : NT (G o_F F) (Id_CAT C);
Prf_Adj1_law1 : Adj1_law1 A_eta A_eps;
Prf_Adj1_law2 : Adj1_law2 A_eta A_eps}.
End adj1_def.
Section adj_to_adj1.
Variables (C D : Category) (F : Functor D C) (G : Functor C D) (ad : Adj F G).
(* *)
Definition Unit_tau (d : D) := UA_mor (Unit ad d).

Lemma Unit_nt_law : NT_law (F:=Id_CAT D) (G:=F o_F G) Unit_tau.
Canonical Structure Unit_NT := Build_NT Unit_nt_law.