diff --git a/Std/Data/RBMap.lean b/Std/Data/RBMap.lean
index 396a2cb6db..93bbf72228 100644
--- a/Std/Data/RBMap.lean
+++ b/Std/Data/RBMap.lean
@@ -1,4 +1,5 @@
 import Std.Data.RBMap.Alter
 import Std.Data.RBMap.Basic
+import Std.Data.RBMap.Depth
 import Std.Data.RBMap.Lemmas
 import Std.Data.RBMap.WF
diff --git a/Std/Data/RBMap/Depth.lean b/Std/Data/RBMap/Depth.lean
new file mode 100644
index 0000000000..da9533781b
--- /dev/null
+++ b/Std/Data/RBMap/Depth.lean
@@ -0,0 +1,85 @@
+/-
+Copyright (c) 2022 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro
+-/
+import Std.Data.RBMap.WF
+
+/-!
+# RBNode depth bounds
+-/
+
+namespace Std.RBNode
+open RBColor
+
+/--
+`O(n)`. `depth t` is the maximum number of nodes on any path to a leaf.
+It is an upper bound on most tree operations.
+-/
+def depth : RBNode α → Nat
+  | nil => 0
+  | node _ a _ b => max a.depth b.depth + 1
+
+theorem size_lt_depth : ∀ t : RBNode α, t.size < 2 ^ t.depth
+  | .nil => (by decide : 0 < 1)
+  | .node _ a _ b => by
+    rw [size, depth, Nat.add_right_comm, Nat.pow_succ, Nat.mul_two]
+    refine Nat.add_le_add
+      (Nat.lt_of_lt_of_le a.size_lt_depth ?_) (Nat.lt_of_lt_of_le b.size_lt_depth ?_)
+    · exact Nat.pow_le_pow_of_le_right (by decide) (Nat.le_max_left ..)
+    · exact Nat.pow_le_pow_of_le_right (by decide) (Nat.le_max_right ..)
+
+/--
+`depthLB c n` is the best upper bound on the depth of any balanced red-black tree
+with root colored `c` and black-height `n`.
+-/
+def depthLB : RBColor → Nat → Nat
+  | red, n => n + 1
+  | black, n => n
+
+theorem depthLB_le : ∀ c n, n ≤ depthLB c n
+  | red, _ => Nat.le_succ _
+  | black, _ => Nat.le_refl _
+
+/--
+`depthUB c n` is the best upper bound on the depth of any balanced red-black tree
+with root colored `c` and black-height `n`.
+-/
+def depthUB : RBColor → Nat → Nat
+  | red, n => 2 * n + 1
+  | black, n => 2 * n
+
+theorem depthUB_le : ∀ c n, depthUB c n ≤ 2 * n + 1
+  | red, _ => Nat.le_refl _
+  | black, _ => Nat.le_succ _
+
+theorem depthUB_le_two_depthLB : ∀ c n, depthUB c n ≤ 2 * depthLB c n
+  | red, _ => Nat.le_succ _
+  | black, _ => Nat.le_refl _
+
+theorem Balanced.depth_le : @Balanced α t c n → t.depth ≤ depthUB c n
+  | .nil => Nat.le_refl _
+  | .red hl hr => Nat.succ_le_succ <| Nat.max_le.2 ⟨hl.depth_le, hr.depth_le⟩
+  | .black hl hr => Nat.succ_le_succ <| Nat.max_le.2
+    ⟨Nat.le_trans hl.depth_le (depthUB_le ..), Nat.le_trans hr.depth_le (depthUB_le ..)⟩
+
+theorem Balanced.le_size : @Balanced α t c n → 2 ^ depthLB c n ≤ t.size + 1
+  | .nil => Nat.le_refl _
+  | .red hl hr => by
+    rw [size, Nat.add_right_comm (size _), Nat.add_assoc, depthLB, Nat.pow_succ, Nat.mul_two]
+    exact Nat.add_le_add hl.le_size hr.le_size
+  | .black hl hr => by
+    rw [size, Nat.add_right_comm (size _), Nat.add_assoc, depthLB, Nat.pow_succ, Nat.mul_two]
+    refine Nat.add_le_add (Nat.le_trans ?_ hl.le_size) (Nat.le_trans ?_ hr.le_size) <;>
+      exact Nat.pow_le_pow_of_le_right (by decide) (depthLB_le ..)
+
+theorem Balanced.depth_bound (h : @Balanced α t c n) : t.depth ≤ 2 * (t.size + 1).log2 :=
+  Nat.le_trans h.depth_le <| Nat.le_trans (depthUB_le_two_depthLB ..) <|
+    Nat.mul_le_mul_left _ <| (Nat.le_log2 (Nat.succ_ne_zero _)).2 h.le_size
+
+/--
+A well formed tree has `t.depth ∈ O(log t.size)`, that is, it is well balanced.
+This justifies the `O(log n)` bounds on most searching operations of `RBSet`.
+-/
+theorem WF.depth_bound {t : RBNode α} (h : t.WF cmp) : t.depth ≤ 2 * (t.size + 1).log2 :=
+  let ⟨_, _, h⟩ := h.out.2; h.depth_bound
diff --git a/Std/Data/RBMap/Lemmas.lean b/Std/Data/RBMap/Lemmas.lean
index 7602d11ca5..40a62df525 100644
--- a/Std/Data/RBMap/Lemmas.lean
+++ b/Std/Data/RBMap/Lemmas.lean
@@ -17,91 +17,6 @@ open RBColor
 
 attribute [simp] fold foldl foldr Any forM foldlM Ordered
 
-section depth
-
-/--
-`O(n)`. `depth t` is the maximum number of nodes on any path to a leaf.
-It is an upper bound on most tree operations.
--/
-def depth : RBNode α → Nat
-  | nil => 0
-  | node _ a _ b => max a.depth b.depth + 1
-
-theorem size_lt_depth : ∀ t : RBNode α, t.size < 2 ^ t.depth
-  | .nil => (by decide : 0 < 1)
-  | .node _ a _ b => by
-    rw [size, depth, Nat.add_right_comm, Nat.pow_succ, Nat.mul_two]
-    refine Nat.add_le_add
-      (Nat.lt_of_lt_of_le a.size_lt_depth ?_) (Nat.lt_of_lt_of_le b.size_lt_depth ?_)
-    · exact Nat.pow_le_pow_of_le_right (by decide) (Nat.le_max_left ..)
-    · exact Nat.pow_le_pow_of_le_right (by decide) (Nat.le_max_right ..)
-
-/--
-`depthLB c n` is the best upper bound on the depth of any balanced red-black tree
-with root colored `c` and black-height `n`.
--/
-def depthLB : RBColor → Nat → Nat
-  | red, n => n + 1
-  | black, n => n
-
-theorem depthLB_le : ∀ c n, n ≤ depthLB c n
-  | red, _ => Nat.le_succ _
-  | black, _ => Nat.le_refl _
-
-/--
-`depthUB c n` is the best upper bound on the depth of any balanced red-black tree
-with root colored `c` and black-height `n`.
--/
-def depthUB : RBColor → Nat → Nat
-  | red, n => 2 * n + 1
-  | black, n => 2 * n
-
-theorem depthUB_le : ∀ c n, depthUB c n ≤ 2 * n + 1
-  | red, _ => Nat.le_refl _
-  | black, _ => Nat.le_succ _
-
-theorem depthUB_le_two_depthLB : ∀ c n, depthUB c n ≤ 2 * depthLB c n
-  | red, _ => Nat.le_succ _
-  | black, _ => Nat.le_refl _
-
-theorem Balanced.depth_le : @Balanced α t c n → t.depth ≤ depthUB c n
-  | .nil => Nat.le_refl _
-  | .red hl hr => Nat.succ_le_succ <| Nat.max_le.2 ⟨hl.depth_le, hr.depth_le⟩
-  | .black hl hr => Nat.succ_le_succ <| Nat.max_le.2
-    ⟨Nat.le_trans hl.depth_le (depthUB_le ..), Nat.le_trans hr.depth_le (depthUB_le ..)⟩
-
-theorem Balanced.le_size : @Balanced α t c n → 2 ^ depthLB c n ≤ t.size + 1
-  | .nil => Nat.le_refl _
-  | .red hl hr => by
-    rw [size, Nat.add_right_comm (size _), Nat.add_assoc, depthLB, Nat.pow_succ, Nat.mul_two]
-    exact Nat.add_le_add hl.le_size hr.le_size
-  | .black hl hr => by
-    rw [size, Nat.add_right_comm (size _), Nat.add_assoc, depthLB, Nat.pow_succ, Nat.mul_two]
-    refine Nat.add_le_add (Nat.le_trans ?_ hl.le_size) (Nat.le_trans ?_ hr.le_size) <;>
-      exact Nat.pow_le_pow_of_le_right (by decide) (depthLB_le ..)
-
-theorem Balanced.depth_bound (h : @Balanced α t c n) : t.depth ≤ 2 * (t.size + 1).log2 :=
-  Nat.le_trans h.depth_le <| Nat.le_trans (depthUB_le_two_depthLB ..) <|
-    Nat.mul_le_mul_left _ <| (Nat.le_log2 (Nat.succ_ne_zero _)).2 h.le_size
-
-/--
-A well formed tree has `t.depth ∈ O(log t.size)`, that is, it is well balanced.
-This justifies the `O(log n)` bounds on most searching operations of `RBSet`.
--/
-theorem WF.depth_bound {t : RBNode α} (h : t.WF cmp) : t.depth ≤ 2 * (t.size + 1).log2 :=
-  let ⟨_, _, h⟩ := h.out.2; h.depth_bound
-
-end depth
-
-@[simp] theorem min?_reverse (t : RBNode α) : t.reverse.min? = t.max? := by
-  unfold RBNode.max?; split <;> simp [RBNode.min?]
-  unfold RBNode.min?; rw [min?.match_1.eq_3]
-  · apply min?_reverse
-  · simpa [reverse_eq_iff]
-
-@[simp] theorem max?_reverse (t : RBNode α) : t.reverse.max? = t.min? := by
-  rw [← min?_reverse, reverse_reverse]
-
 @[simp] theorem mem_nil {x} : ¬x ∈ (.nil : RBNode α) := by simp [(·∈·), EMem]
 @[simp] theorem mem_node {y c a x b} :
     y ∈ (.node c a x b : RBNode α) ↔ y = x ∨ y ∈ a ∨ y ∈ b := by simp [(·∈·), EMem]