🎨 Small renames for consistency

Rubin.lean

@@ -58,7 +58,7 @@ structure RubinAction (G α : Type _) extends
 where
   locally_compact : LocallyCompactSpace α
   hausdorff : T2Space α
-  no_isolated_points : Rubin.has_no_isolated_points α
+  no_isolated_points : HasNoIsolatedPoints α
   locallyDense : LocallyDense G α
 #align rubin_action Rubin.RubinAction
 
@@ -97,7 +97,7 @@ by
     rw [h_in_ristV _ x_notin_V]
   let ⟨q, q_in_V, hq_ne_q ⟩ := faithful_rigid_stabilizer_moves_point h_in_ristV h_ne_one
   have gpowi_q_notin_V : ∀ (i : Fin n), (i : ℕ) > 0 → g ^ (i : ℕ) • q ∉ V := by
-    apply smulImage_distinct_of_disjoint_exp n_pos disj
+    apply smulImage_distinct_of_disjoint_pow n_pos disj
     exact q_in_V
 
   -- We have (hg)^i q = g^i q for all 0 < i < n
@@ -122,7 +122,7 @@ by
       let i'₂ : Fin n := ⟨Nat.succ i', i_lt_n⟩
       have h_eq: Nat.succ i' = (i'₂ : ℕ) := by simp
       rw [h_eq]
-      apply smulImage_distinct_of_disjoint_exp
+      apply smulImage_distinct_of_disjoint_pow
       · exact n_pos
       · exact disj
       · exact q_in_V
@@ -246,7 +246,7 @@ by
   apply not_support_subset_rsupp
   show Support α h ⊆ RegularSupport α f
 
-  apply subset_of_diff_closure_regular_empty
+  apply subset_from_diff_closure_eq_empty
   · apply regularSupport_regular
   · exact support_open _
   · rw [Set.not_nonempty_iff_eq_empty] at U_empty

Rubin/AlgebraicDisjointness.lean

@@ -156,7 +156,7 @@ variable [ContinuousMulAction G α]
 variable [FaithfulSMul G α]
 
 instance dense_locally_moving [T2Space α]
-  (H_nip : has_no_isolated_points α)
+  [H_nip : HasNoIsolatedPoints α]
   (H_ld : LocallyDense G α) :
   LocallyMoving G α
 where
@@ -164,7 +164,8 @@ where
     intros U _ H_nonempty
     by_contra h_rs
     have ⟨elem, ⟨_, some_in_orbit⟩⟩ := H_ld.nonEmpty H_nonempty
-    have H_nebot := has_no_isolated_points_neBot H_nip elem
+    -- Note: This is automatic now :)
+    -- have H_nebot := has_no_isolated_points_neBot elem
     rw [h_rs] at some_in_orbit
     simp at some_in_orbit
 
@@ -326,9 +327,6 @@ lemma proposition_1_1_1 [h_lm : LocallyMoving G α] [T2Space α] (f g : G) (supp
     exact z_moved h₆
 #align proposition_1_1_1 Rubin.proposition_1_1_1
 
-@[simp] lemma smulImage_mul {g h : G} {U : Set α} : g •'' (h •'' U) = (g*h) •'' U :=
-  (mul_smulImage g h U)
-
 lemma smul_inj_moves {ι : Type*} [Fintype ι] [T2Space α]
   {f : ι → G} {x : α} {i j : ι} (i_ne_j : i ≠ j)
   (f_smul_inj : Function.Injective (fun i : ι => (f i) • x)) :
@@ -682,12 +680,12 @@ by
   clear f₁_commutes f₂_commutes
 
   have g_k_disjoint : Disjoint ((g^i.val)⁻¹ •'' (k •'' V)) ((g^j.val)⁻¹ •'' (k •'' V)) := by
-    repeat rw [mul_smulImage]
+    repeat rw [smulImage_mul]
     repeat rw [<-inv_pow]
     repeat rw [k_commutes.symm.inv_left.pow_left]
-    repeat rw [<-mul_smulImage k]
+    repeat rw [<-smulImage_mul k]
     repeat rw [inv_pow]
-    exact disjoint_smulImage k g_disjoint
+    exact smulImage_disjoint k g_disjoint
 
   apply Set.disjoint_left.mp g_k_disjoint
   · rw [mem_inv_smulImage]

Rubin/InteriorClosure.lean

@@ -0,0 +1,160 @@
+import Mathlib.Topology.Basic
+import Mathlib.Topology.Separation
+
+namespace Rubin
+
+variable {α : Type _}
+variable [TopologicalSpace α]
+
+/--
+Defines a kind of "regularization" transformation made to sets,
+by calling `closure` followed by `interior` on those sets.
+
+A set is then said to be [`Regular`] if the InteriorClosure does not modify it.
+--/
+def InteriorClosure (U : Set α) : Set α :=
+  interior (closure U)
+#align interior_closure Rubin.InteriorClosure
+
+@[simp]
+theorem InteriorClosure.def (U : Set α) : InteriorClosure U = interior (closure U) :=
+  by simp [InteriorClosure]
+
+@[simp]
+theorem InteriorClosure.fdef : InteriorClosure = (interior ∘ (closure (α := α))) := by ext; simp
+
+/--
+A set `U` is said to be regular if the interior of the closure of `U` is equal to `U`.
+Notably, a regular set is also open, and the interior of a regular set is equal to itself.
+--/
+def Regular (U : Set α) : Prop :=
+  InteriorClosure U = U
+
+@[simp]
+theorem Regular.def (U : Set α) : Regular U ↔ interior (closure U) = U :=
+  by simp [Regular]
+#align set.is_regular_def Rubin.Regular.def
+
+@[simp]
+theorem Regular.eq {U : Set α} (U_reg : Regular U) : interior (closure U) = U :=
+  (Regular.def U).mp U_reg
+
+instance Regular.instCoe {U : Set α} : Coe (Regular U) (interior (closure U) = U) where
+  coe := Regular.eq
+
+/-- From this, the set of regular sets is the set of regular *open* sets. --/
+theorem regular_open (U : Set α) : Regular U → IsOpen U :=
+by
+  intro h_reg
+  rw [<-h_reg]
+  simp
+
+theorem Regular.isOpen {U : Set α} (U_regular : Regular U): IsOpen U := regular_open _ U_regular
+
+theorem regular_interior {U : Set α} : Regular U → interior U = U :=
+by
+  intro h_reg
+  rw [<-h_reg]
+  simp
+
+theorem interiorClosure_open (U : Set α) : IsOpen (InteriorClosure U) := by simp
+#align is_open_interior_closure Rubin.interiorClosure_open
+
+theorem interiorClosure_subset {U : Set α} :
+  IsOpen U → U ⊆ InteriorClosure U :=
+by
+  intro h
+  apply subset_trans
+  exact subset_interior_iff_isOpen.mpr h
+  apply interior_mono
+  exact subset_closure
+#align is_open.interior_closure_subset Rubin.interiorClosure_subset
+
+theorem interiorClosure_regular (U : Set α) : Regular (InteriorClosure U) :=
+by
+  apply Set.eq_of_subset_of_subset <;> unfold InteriorClosure
+  {
+    apply interior_mono
+    nth_rw 2 [<-closure_closure (s := U)]
+    apply closure_mono
+    exact interior_subset
+  }
+  {
+    nth_rw 1 [<-interior_interior]
+    apply interior_mono
+    exact subset_closure
+  }
+#align regular_interior_closure Rubin.interiorClosure_regular
+
+theorem interiorClosure_mono (U V : Set α) :
+  U ⊆ V → InteriorClosure U ⊆ InteriorClosure V
+:= interior_mono ∘ closure_mono
+#align interior_closure_mono Rubin.interiorClosure_mono
+
+theorem monotone_interiorClosure : Monotone (InteriorClosure (α := α))
+:= fun a b =>
+  interiorClosure_mono a b
+
+theorem compl_closure_regular_of_open {S : Set α} (S_open : IsOpen S) : Regular (closure S)ᶜ := by
+  apply Set.eq_of_subset_of_subset
+  · simp
+    apply closure_mono
+    rw [IsOpen.subset_interior_iff S_open]
+    exact subset_closure
+  · apply interiorClosure_subset
+    simp
+
+@[simp]
+theorem interiorClosure_closure {S : Set α} (S_open : IsOpen S) : closure (InteriorClosure S) = closure S :=
+by
+  apply Set.eq_of_subset_of_subset
+  · simp
+    rw [<-Set.compl_subset_compl]
+    rw [<-(compl_closure_regular_of_open S_open)]
+    simp
+    rfl
+  · apply closure_mono
+    exact interiorClosure_subset S_open
+
+@[simp]
+theorem interiorClosure_interior {S : Set α} : interior (InteriorClosure S) = (InteriorClosure S) :=
+regular_interior (interiorClosure_regular S)
+
+theorem disjoint_interiorClosure_left {U V : Set α} (V_open : IsOpen V)
+  (disj : Disjoint U V) : Disjoint (InteriorClosure U) V :=
+by
+  apply Set.disjoint_of_subset_left interior_subset
+  exact Disjoint.closure_left disj V_open
+
+theorem disjoint_interiorClosure_right {U V : Set α} (U_open : IsOpen U)
+  (disj : Disjoint U V) : Disjoint U (InteriorClosure V) :=
+  (disjoint_interiorClosure_left U_open (Disjoint.symm disj)).symm
+
+theorem subset_from_diff_closure_eq_empty {U V : Set α}
+  (U_regular : Regular U) (V_open : IsOpen V) (V_diff_cl_empty : V \ closure U = ∅) :
+  V ⊆ U :=
+by
+  have V_eq_interior : interior V = V := IsOpen.interior_eq V_open
+  rw [<-V_eq_interior]
+  rw [<-U_regular]
+  apply interior_mono
+  rw [<-Set.diff_eq_empty]
+  exact V_diff_cl_empty
+
+theorem regular_nbhd [T2Space α] {u v : α} (u_ne_v : u ≠ v):
+  ∃ (U V : Set α), Regular U ∧ Regular V ∧ Disjoint U V ∧ u ∈ U ∧ v ∈ V :=
+by
+  let ⟨U', V', U'_open, V'_open, u_in_U', v_in_V', disj⟩ := t2_separation u_ne_v
+  let U := InteriorClosure U'
+  let V := InteriorClosure V'
+  use U, V
+  repeat' apply And.intro
+  · apply interiorClosure_regular
+  · apply interiorClosure_regular
+  · apply disjoint_interiorClosure_left (interiorClosure_regular V').isOpen
+    apply disjoint_interiorClosure_right U'_open
+    exact disj
+  · exact (interiorClosure_subset U'_open) u_in_U'
+  · exact (interiorClosure_subset V'_open) v_in_V'
+
+end Rubin

Rubin/RegularSupport.lean

@@ -7,98 +7,10 @@ import Mathlib.Topology.Separation
 import Rubin.Tactic
 import Rubin.Support
 import Rubin.Topological
+import Rubin.InteriorClosure
 
 namespace Rubin
 
-section InteriorClosure
-
-variable {α : Type _}
-variable [TopologicalSpace α]
-
--- Defines a kind of "regularization" transformation made to sets,
--- by calling `closure` followed by `interior` on it.
---
--- A set is then said to be regular if the InteriorClosure does not modify it.
-def InteriorClosure (U : Set α) : Set α :=
-  interior (closure U)
-#align interior_closure Rubin.InteriorClosure
-
-@[simp]
-theorem InteriorClosure.def (U : Set α) : InteriorClosure U = interior (closure U) :=
-  by simp [InteriorClosure]
-
-@[simp]
-theorem InteriorClosure.fdef : InteriorClosure = (interior ∘ (closure (α := α))) := by ext; simp
-
--- A set `U` is said to be regular if the interior of the closure of `U` is equal to `U`.
--- Notably, a regular set is also open, and the interior of a regular set is equal to itself.
-def Regular (U : Set α) : Prop :=
-  InteriorClosure U = U
-
-@[simp]
-theorem Regular.def (U : Set α) : Regular U ↔ interior (closure U) = U :=
-  by simp [Regular]
-#align set.is_regular_def Rubin.Regular.def
-
-@[simp]
-theorem Regular.eq {U : Set α} (U_reg : Regular U) : interior (closure U) = U :=
-  (Regular.def U).mp U_reg
-
-instance Regular.instCoe {U : Set α} : Coe (Regular U) (interior (closure U) = U) where
-  coe := Regular.eq
-
-theorem interiorClosure_open (U : Set α) : IsOpen (InteriorClosure U) := by simp
-#align is_open_interior_closure Rubin.interiorClosure_open
-
-theorem interiorClosure_subset {U : Set α} :
-  IsOpen U → U ⊆ InteriorClosure U :=
-by
-  intro h
-  apply subset_trans
-  exact subset_interior_iff_isOpen.mpr h
-  apply interior_mono
-  exact subset_closure
-#align is_open.interior_closure_subset Rubin.interiorClosure_subset
-
-theorem interiorClosure_regular (U : Set α) : Regular (InteriorClosure U) :=
-by
-  apply Set.eq_of_subset_of_subset <;> unfold InteriorClosure
-  {
-    apply interior_mono
-    nth_rw 2 [<-closure_closure (s := U)]
-    apply closure_mono
-    exact interior_subset
-  }
-  {
-    nth_rw 1 [<-interior_interior]
-    apply interior_mono
-    exact subset_closure
-  }
-#align regular_interior_closure Rubin.interiorClosure_regular
-
-theorem interiorClosure_mono (U V : Set α) :
-  U ⊆ V → InteriorClosure U ⊆ InteriorClosure V
-:= interior_mono ∘ closure_mono
-#align interior_closure_mono Rubin.interiorClosure_mono
-
-theorem monotone_interior_closure : Monotone (InteriorClosure (α := α))
-:= fun a b =>
-  interiorClosure_mono a b
-
-theorem regular_open (U : Set α) : Regular U → IsOpen U :=
-by
-  intro h_reg
-  rw [<-h_reg]
-  simp
-
-theorem regular_interior (U : Set α) : Regular U → interior U = U :=
-by
-  intro h_reg
-  rw [<-h_reg]
-  simp
-
-end InteriorClosure
-
 section RegularSupport_def
 
 variable {G : Type _}

Rubin/SmulImage.lean

@@ -66,14 +66,13 @@ by
   rw [mem_smulImage]
   rw [<-mul_smul, mul_left_inv, one_smul]
 
--- TODO: rename to smulImage_mul
 @[simp]
-theorem mul_smulImage (g h : G) (U : Set α) : g •'' (h •'' U) = (g * h) •'' U :=
+theorem smulImage_mul (g h : G) (U : Set α) : g •'' (h •'' U) = (g * h) •'' U :=
   by
   ext
   rw [Rubin.mem_smulImage, Rubin.mem_smulImage, Rubin.mem_smulImage, ←
     mul_smul, mul_inv_rev]
-#align mul_smul'' Rubin.mul_smulImage
+#align mul_smul'' Rubin.smulImage_mul
 
 @[simp]
 theorem one_smulImage (U : Set α) : (1 : G) •'' U = U :=
@@ -82,7 +81,7 @@ theorem one_smulImage (U : Set α) : (1 : G) •'' U = U :=
   rw [Rubin.mem_smulImage, inv_one, one_smul]
 #align one_smul'' Rubin.one_smulImage
 
-theorem disjoint_smulImage (g : G) {U V : Set α} :
+theorem smulImage_disjoint (g : G) {U V : Set α} :
     Disjoint U V → Disjoint (g •'' U) (g •'' V) :=
   by
   intro disjoint_U_V
@@ -91,13 +90,23 @@ theorem disjoint_smulImage (g : G) {U V : Set α} :
   intro x x_in_gU
   by_contra h
   exact (disjoint_U_V (mem_smulImage.mp x_in_gU)) (mem_smulImage.mp h)
-#align disjoint_smul'' Rubin.disjoint_smulImage
+#align disjoint_smul'' Rubin.smulImage_disjoint
 
-namespace SmulImage
-theorem congr (g : G) {U V : Set α} : U = V → g •'' U = g •'' V :=
+theorem SmulImage.congr (g : G) {U V : Set α} : U = V → g •'' U = g •'' V :=
   congr_arg fun W : Set α => g •'' W
 #align smul''_congr Rubin.SmulImage.congr
-end SmulImage
+
+theorem SmulImage.inv_congr (g: G) {U V : Set α} : g •'' U = g •'' V → U = V :=
+by
+  intro h
+  rw [<-one_smulImage (G := G) U]
+  rw [<-one_smulImage (G := G) V]
+  rw [<-mul_left_inv g]
+  repeat rw [<-smulImage_mul]
+  exact SmulImage.congr g⁻¹ h
+
+theorem smulImage_inv {g: G} {U V : Set α} (img_eq : g •'' U = g •'' V) : U = V :=
+  SmulImage.inv_congr g img_eq
 
 theorem smulImage_subset (g : G) {U V : Set α} : U ⊆ V → g •'' U ⊆ g •'' V :=
   by
@@ -149,12 +158,12 @@ by
   constructor
   · intro h
     apply smulImage_subset f⁻¹ at h
-    rw [mul_smulImage] at h
+    rw [smulImage_mul] at h
     rw [mul_left_inv, one_smulImage] at h
     exact h
   · intro h
     apply smulImage_subset f at h
-    rw [mul_smulImage] at h
+    rw [smulImage_mul] at h
     rw [mul_right_inv, one_smulImage] at h
     exact h
 
@@ -170,14 +179,14 @@ theorem smulImage_disjoint_mul {G α : Type _} [Group G] [MulAction G α]
   Disjoint (f •'' U) (g •'' V) ↔ Disjoint U ((f⁻¹ * g) •'' V) := by
   constructor
   · intro h
-    apply disjoint_smulImage f⁻¹ at h
-    repeat rw [mul_smulImage] at h
+    apply smulImage_disjoint f⁻¹ at h
+    repeat rw [smulImage_mul] at h
     rw [mul_left_inv, one_smulImage] at h
     exact h
 
   · intro h
-    apply disjoint_smulImage f at h
-    rw [mul_smulImage] at h
+    apply smulImage_disjoint f at h
+    rw [smulImage_mul] at h
     rw [<-mul_assoc] at h
     rw [mul_right_inv, one_mul] at h
     exact h
@@ -200,7 +209,7 @@ by
 
 -- States that if `g^i •'' V` and `g^j •'' V` are disjoint for any `i ≠ j` and `x ∈ V`
 -- then `g^i • x` will always lie outside of `V`.
-lemma smulImage_distinct_of_disjoint_exp {G α : Type _} [Group G] [MulAction G α] {g : G} {V : Set α} {n : ℕ}
+lemma smulImage_distinct_of_disjoint_pow {G α : Type _} [Group G] [MulAction G α] {g : G} {V : Set α} {n : ℕ}
   (n_pos : 0 < n)
   (h_disj : ∀ (i j : Fin n), i ≠ j → Disjoint (g ^ (i : ℕ) •'' V) (g ^ (j : ℕ) •'' V)) :
   ∀ (x : α) (_hx : x ∈ V) (i : Fin n), 0 < (i : ℕ) → g ^ (i : ℕ) • (x : α) ∉ V :=
@@ -216,6 +225,6 @@ by
   have h_notin_V := Set.disjoint_left.mp (h_disj i (⟨0, n_pos⟩ : Fin n) i_ne_zero) h_contra
   simp only [pow_zero, one_smulImage] at h_notin_V
   exact h_notin_V
-#align distinct_images_from_disjoint Rubin.smulImage_distinct_of_disjoint_exp
+#align distinct_images_from_disjoint Rubin.smulImage_distinct_of_disjoint_pow
 
 end Rubin

Rubin/Topological.lean

@@ -46,7 +46,7 @@ theorem equivariant_inv [MulAction G α] [MulAction G β]
   exact e
 #align equivariant_inv Rubin.equivariant_inv
 
-variable [Rubin.ContinuousMulAction G α]
+variable [ContinuousMulAction G α]
 
 theorem img_open_open (g : G) (U : Set α) (h : IsOpen U): IsOpen (g •'' U) :=
   by
@@ -56,7 +56,7 @@ theorem img_open_open (g : G) (U : Set α) (h : IsOpen U): IsOpen (g •'' U) :=
 #align img_open_open Rubin.img_open_open
 
 theorem support_open (g : G) [TopologicalSpace α] [T2Space α]
-    [Rubin.ContinuousMulAction G α] : IsOpen (Support α g) :=
+    [ContinuousMulAction G α] : IsOpen (Support α g) :=
   by
   apply isOpen_iff_forall_mem_open.mpr
   intro x xmoved
@@ -75,17 +75,19 @@ theorem support_open (g : G) [TopologicalSpace α] [T2Space α]
 end Continuity
 
 -- TODO: come up with a name
-section Other
+section LocallyDense
 open Topology
 
--- Note: `𝓝[≠] x` is notation for `nhdsWithin x {[x]}ᶜ`, ie. the neighborhood of x not containing itself
--- TODO: make this a class?
-def has_no_isolated_points (α : Type _) [TopologicalSpace α] :=
-  ∀ x : α, 𝓝[≠] x ≠ ⊥
-#align has_no_isolated_points Rubin.has_no_isolated_points
+/--
+Note: `𝓝[≠] x` is notation for `nhdsWithin x {[x]}ᶜ`, ie. the neighborhood of x not containing itself.
 
-instance has_no_isolated_points_neBot {α : Type _} [TopologicalSpace α] (h_nip: has_no_isolated_points α) (x: α): Filter.NeBot (𝓝[≠] x) where
-  ne' := h_nip x
+--/
+class HasNoIsolatedPoints (α : Type _) [TopologicalSpace α] :=
+  nhbd_ne_bot : ∀ x : α, 𝓝[≠] x ≠ ⊥
+#align has_no_isolated_points Rubin.HasNoIsolatedPoints
+
+instance has_no_isolated_points_neBot {α : Type _} [TopologicalSpace α] [h_nip: HasNoIsolatedPoints α] (x: α): Filter.NeBot (𝓝[≠] x) where
+  ne' := h_nip.nhbd_ne_bot x
 
 class LocallyDense (G α : Type _) [Group G] [TopologicalSpace α] extends MulAction G α :=
   isLocallyDense:
@@ -97,48 +99,12 @@ class LocallyDense (G α : Type _) [Group G] [TopologicalSpace α] extends MulAc
 lemma LocallyDense.nonEmpty {G α : Type _} [Group G] [TopologicalSpace α] [LocallyDense G α]:
   ∀ {U : Set α},
   Set.Nonempty U →
-  ∃ p ∈ U, p ∈ interior (closure (MulAction.orbit (RigidStabilizer G U) p)) := by
+  ∃ p ∈ U, p ∈ interior (closure (MulAction.orbit (RigidStabilizer G U) p)) :=
+by
   intros U H_ne
   exact ⟨H_ne.some, H_ne.some_mem, LocallyDense.isLocallyDense U H_ne.some H_ne.some_mem⟩
 
--- Should be put into mathlib — it doesn't use constructive logic only,
--- unlike (I assume) the inter_compl_nonempty_iff counterpart
-lemma Set.inter_compl_empty_iff {α : Type _} (s t : Set α) :
-  s ∩ tᶜ = ∅ ↔ s ⊆ t :=
-by
-  constructor
-  {
-    intro h₁
-    by_contra h₂
-    rw [<-Set.inter_compl_nonempty_iff] at h₂
-    rw [Set.nonempty_iff_ne_empty] at h₂
-    exact h₂ h₁
-  }
-  {
-    intro h₁
-    by_contra h₂
-    rw [<-ne_eq, <-Set.nonempty_iff_ne_empty] at h₂
-    rw [Set.inter_compl_nonempty_iff] at h₂
-    exact h₂ h₁
-  }
-
-theorem subset_of_diff_closure_regular_empty {α : Type _} [TopologicalSpace α] {U V : Set α}
-  (U_regular : interior (closure U) = U) (V_open : IsOpen V) (V_diff_cl_empty : V \ closure U = ∅) :
-  V ⊆ U :=
-by
-  have V_eq_interior : interior V = V := IsOpen.interior_eq V_open
-  -- rw [<-V_eq_interior]
-  have V_subset_closure_U : V ⊆ closure U := by
-    rw [Set.diff_eq_compl_inter] at V_diff_cl_empty
-    rw [Set.inter_comm] at V_diff_cl_empty
-    rw [Set.inter_compl_empty_iff] at V_diff_cl_empty
-    exact V_diff_cl_empty
-  have res : interior V ⊆ interior (closure U) := interior_mono V_subset_closure_U
-  rw [U_regular] at res
-  rw [V_eq_interior] at res
-  exact res
-
-
-end Other
+end LocallyDense
+
 
 end Rubin