chore(CategoryTheory/Adjunction/Opposites): redefine the opposite of an adjunction (#20375)

Change the definition of `Adjunction.adjointOfOpAdjointOp` and `Adjunction.opAdjointOpOfAdjoint` to be more in line with the new definition of adjunctions from #16317 (which removes the `homEquiv` field), and rename these to `Adjunction.op` and `Adjunction.unop` to be consistent with `Equivalence.op` and `Equivalence.unop`. The 6 other variants of opposite adjunctions are all defined from `Adjunction.op` or `Adjunction.unop` and should not be needed anymore, they have been marked as `deprecated`, as well as `Adjunction.adjointOfOpAdjointOp` and `Adjunction.opAdjointOpOfAdjoint`.



Co-authored-by: smorel394 <67864981+smorel394@users.noreply.github.com>

Author: smorel394

Mathlib/CategoryTheory/Adjunction/Opposites.lean

@@ -29,66 +29,31 @@ namespace CategoryTheory.Adjunction
 
 attribute [local simp] homEquiv_unit homEquiv_counit
 
-/-- If `G.op` is adjoint to `F.op` then `F` is adjoint to `G`. -/
-@[simps! unit_app counit_app]
-def adjointOfOpAdjointOp (F : C ⥤ D) (G : D ⥤ C) (h : G.op ⊣ F.op) : F ⊣ G :=
-  Adjunction.mkOfHomEquiv {
-    homEquiv := fun {X Y} =>
-      ((h.homEquiv (Opposite.op Y) (Opposite.op X)).trans (opEquiv _ _)).symm.trans
-        (opEquiv _ _)
-    homEquiv_naturality_left_symm := by
-      -- Porting note: This proof was handled by `obviously` in mathlib3. The only obstruction to
-      -- automation fully kicking in here is that the `@[simps]` lemmas of `opEquiv` and
-      -- `homEquiv` aren't firing.
-      intros
-      simp [opEquiv, homEquiv]
-    homEquiv_naturality_right := by
-      -- Porting note: This proof was handled by `obviously` in mathlib3. The only obstruction to
-      -- automation fully kicking in here is that the `@[simps]` lemmas of `opEquiv` and
-      -- `homEquiv` aren't firing.
-      intros
-      simp [opEquiv, homEquiv] }
-
-/-- If `G` is adjoint to `F.op` then `F` is adjoint to `G.unop`. -/
-def adjointUnopOfAdjointOp (F : C ⥤ D) (G : Dᵒᵖ ⥤ Cᵒᵖ) (h : G ⊣ F.op) : F ⊣ G.unop :=
-  adjointOfOpAdjointOp F G.unop (h.ofNatIsoLeft G.opUnopIso.symm)
-
-/-- If `G.op` is adjoint to `F` then `F.unop` is adjoint to `G`. -/
-def unopAdjointOfOpAdjoint (F : Cᵒᵖ ⥤ Dᵒᵖ) (G : D ⥤ C) (h : G.op ⊣ F) : F.unop ⊣ G :=
-  adjointOfOpAdjointOp _ _ (h.ofNatIsoRight F.opUnopIso.symm)
-
 /-- If `G` is adjoint to `F` then `F.unop` is adjoint to `G.unop`. -/
-def unopAdjointUnopOfAdjoint (F : Cᵒᵖ ⥤ Dᵒᵖ) (G : Dᵒᵖ ⥤ Cᵒᵖ) (h : G ⊣ F) : F.unop ⊣ G.unop :=
-  adjointUnopOfAdjointOp F.unop G (h.ofNatIsoRight F.opUnopIso.symm)
+@[simps]
+def unop {F : Cᵒᵖ ⥤ Dᵒᵖ} {G : Dᵒᵖ ⥤ Cᵒᵖ} (h : G ⊣ F) : F.unop ⊣ G.unop where
+  unit := NatTrans.unop h.counit
+  counit := NatTrans.unop h.unit
+  left_triangle_components _ := Quiver.Hom.op_inj (h.right_triangle_components _)
+  right_triangle_components _ := Quiver.Hom.op_inj (h.left_triangle_components _)
+
+@[deprecated (since := "2025-01-01")] alias adjointOfOpAdjointOp := unop
+@[deprecated (since := "2025-01-01")] alias adjointUnopOfAdjointOp := unop
+@[deprecated (since := "2025-01-01")] alias unopAdjointOfOpAdjoint := unop
+@[deprecated (since := "2025-01-01")] alias unopAdjointUnopOfAdjoint := unop
 
 /-- If `G` is adjoint to `F` then `F.op` is adjoint to `G.op`. -/
-@[simps! unit_app counit_app]
-def opAdjointOpOfAdjoint (F : C ⥤ D) (G : D ⥤ C) (h : G ⊣ F) : F.op ⊣ G.op :=
-  Adjunction.mkOfHomEquiv {
-    homEquiv := fun X Y =>
-      (opEquiv _ Y).trans ((h.homEquiv _ _).symm.trans (opEquiv X (Opposite.op _)).symm)
-    homEquiv_naturality_left_symm := by
-      -- Porting note: This proof was handled by `obviously` in mathlib3. The only obstruction to
-      -- automation fully kicking in here is that the `@[simps]` lemmas of `opEquiv` aren't firing.
-      intros
-      simp [opEquiv]
-    homEquiv_naturality_right := by
-      -- Porting note: This proof was handled by `obviously` in mathlib3. The only obstruction to
-      -- automation fully kicking in here is that the `@[simps]` lemmas of `opEquiv` aren't firing.
-      intros
-      simp [opEquiv] }
-
-/-- If `G` is adjoint to `F.unop` then `F` is adjoint to `G.op`. -/
-def adjointOpOfAdjointUnop (F : Cᵒᵖ ⥤ Dᵒᵖ) (G : D ⥤ C) (h : G ⊣ F.unop) : F ⊣ G.op :=
-  (opAdjointOpOfAdjoint F.unop _ h).ofNatIsoLeft F.opUnopIso
-
-/-- If `G.unop` is adjoint to `F` then `F.op` is adjoint to `G`. -/
-def opAdjointOfUnopAdjoint (F : C ⥤ D) (G : Dᵒᵖ ⥤ Cᵒᵖ) (h : G.unop ⊣ F) : F.op ⊣ G :=
-  (opAdjointOpOfAdjoint _ G.unop h).ofNatIsoRight G.opUnopIso
-
-/-- If `G.unop` is adjoint to `F.unop` then `F` is adjoint to `G`. -/
-def adjointOfUnopAdjointUnop (F : Cᵒᵖ ⥤ Dᵒᵖ) (G : Dᵒᵖ ⥤ Cᵒᵖ) (h : G.unop ⊣ F.unop) : F ⊣ G :=
-  (adjointOpOfAdjointUnop _ _ h).ofNatIsoRight G.opUnopIso
+@[simps]
+def op {F : C ⥤ D} {G : D ⥤ C} (h : G ⊣ F) : F.op ⊣ G.op where
+  unit := NatTrans.op h.counit
+  counit := NatTrans.op h.unit
+  left_triangle_components _ := Quiver.Hom.unop_inj (by simp)
+  right_triangle_components _ := Quiver.Hom.unop_inj (by simp)
+
+@[deprecated (since := "2025-01-01")] alias opAdjointOpOfAdjoint := op
+@[deprecated (since := "2025-01-01")] alias adjointOpOfAdjointUnop := op
+@[deprecated (since := "2025-01-01")] alias opAdjointOfUnopAdjoint := op
+@[deprecated (since := "2025-01-01")] alias adjointOfUnopAdjointUnop := op
 
 /-- If `F` and `F'` are both adjoint to `G`, there is a natural isomorphism
 `F.op ⋙ coyoneda ≅ F'.op ⋙ coyoneda`.
@@ -119,7 +84,6 @@ Note: it is generally better to use `Adjunction.natIsoEquiv`, see the file `Adju
 -/
 def natIsoOfLeftAdjointNatIso {F F' : C ⥤ D} {G G' : D ⥤ C}
     (adj1 : F ⊣ G) (adj2 : F' ⊣ G') (l : F ≅ F') : G ≅ G' :=
-  NatIso.removeOp (natIsoOfRightAdjointNatIso (opAdjointOpOfAdjoint _ F' adj2)
-    (opAdjointOpOfAdjoint _ _ adj1) (NatIso.op l))
+  NatIso.removeOp (natIsoOfRightAdjointNatIso (op adj2) (op adj1) (NatIso.op l))
 
 end CategoryTheory.Adjunction