diff --git a/notes.md b/notes.md
index 6a579f0..03a707f 100644
--- a/notes.md
+++ b/notes.md
@@ -246,15 +246,13 @@ insertion and search.
 
 ## Growing a *chained hash table*
 
-In order to grow a table, a new table must be created. The hash function (or it
-s
-range parameters) must be changed as well.
+In order to grow a table, a new table must be created. The hash function (or
+its range parameters) must be changed as well.
 
 ### Rehashing
 
 *Rehashing* is the process of putting all the elements of the old table in the
-new
-table according to the new hash function. The complexity is O(n), since
+new table according to the new hash function. The complexity is O(n), since
 `Chained-hash-insert` is constant.
 
 ### Growing the table every time
@@ -279,4 +277,40 @@ that has ...)
 - `Tree-Search(T, k)` returns if key K is in the tree T;
 - `Tree-Minimum(T)` finds the smallest element in the tree;
 - `Tree-Maximum(T)` finds the biggest element in the tree;
-- `Tree-successor(T, k)` `Tree-predecessor(T, k)
+- `Tree-successor(T, k)` and `Tree-predecessor(T, k)` find the next and
+  previous position in the tree
+
+## Height of a tree
+
+The height of a tree is the maximum number of edges traversed from parent to
+child in order to reach a leaf from the root of the tree.
+
+## Rotation
+
+```
+                b
+            /       \
+          a           \
+       /      \         \
+     /          \         \
+k <= a     a <= k <= b     k >= b
+```
+
+```
+               a
+           /       \
+         /            b
+       /          /       \
+     /          /           \
+k <= a     a <= k <= b     k >= b
+```
+
+# Red-Black trees
+
+1. Every node has a color: red or black
+2. The root is black
+3. Every NULL leaf node is black
+4. If a node is red, both of its children are black
+5. The black height is the same for every branch in the tree
+
+A red node is a way to strech the tree, but the
diff --git a/partition.py b/partition.py
index 039f4c4..c455ffa 100755
--- a/partition.py
+++ b/partition.py
@@ -1,37 +1,40 @@
 #!/usr/bin/env python3
+# vim: set ts=2 sw=2 et tw=80:
 
 import sys
 import random
 
+
 def partition(A, begin, end):
-    v_i = random.randrange(begin, end)
-    v = A[v_i]
-    A[v_i], A[end-1] = A[end-1], A[v_i]
-    i = begin
-    j = end - 2
-    while j >= i:
-        if A[j] > v:
-            j = j - 1
-        elif A[i] <= v:
-            i = i + 1
-        else:
-            A[i], A[j] = A[j], A[i]
-            j = j - 1
-            i = i + 1
-    A[i], A[end-1] = A[end-1], A[i]
-    return i
+  v_i = random.randrange(begin, end)
+  v = A[v_i]
+  A[v_i], A[end - 1] = A[end - 1], A[v_i]
+  i = begin
+  j = end - 2
+  while j >= i:
+    if A[j] > v:
+      j = j - 1
+    elif A[i] <= v:
+      i = i + 1
+    else:
+      A[i], A[j] = A[j], A[i]
+      j = j - 1
+      i = i + 1
+  A[i], A[end - 1] = A[end - 1], A[i]
+  return i
+
 
 def quicksort(A, begin, end):
-    if begin < end - 1:
-        i = partition(A, begin, end)
-        print(A[begin:i], A[i], A[i+1:end])
-        quicksort(A, begin, i)
-        quicksort(A, i+1, end)
-        print(A[begin:i], A[i], A[i+1:end])
+  if begin < end - 1:
+    i = partition(A, begin, end)
+    print(A[begin:i], A[i], A[i + 1:end])
+    quicksort(A, begin, i)
+    quicksort(A, i + 1, end)
+    print(A[begin:i], A[i], A[i + 1:end])
+
 
 if __name__ == "__main__":
-    args = [int(x) for x in sys.argv[1:]]
-    print(args)
-    quicksort(args, 0, len(args))
-    print(args)
-
+  args = [int(x) for x in sys.argv[1:]]
+  print(args)
+  quicksort(args, 0, len(args))
+  print(args)
diff --git a/tree.py b/tree.py
index eb849d5..b2fabfa 100644
--- a/tree.py
+++ b/tree.py
@@ -1,10 +1,210 @@
 #!/usr/bin/env python3
 # vim: set ts=2 sw=2 et tw=80:
 
+import sys
+
+
 class Node:
   def __init__(self, k):
     self.key = k
     self.left = None
     self.right = None
+    self.parent = None
+
+  def set_left(self, kNode):
+    kNode.parent = self
+    self.left = kNode
+
+  def set_right(self, kNode):
+    kNode.parent = self
+    self.right = kNode
 
 
+tree = Node(77)
+tree.set_left(Node(30))
+tree.left.set_left(Node(21))
+tree.left.set_right(Node(33))
+tree.left.right.set_left(Node(31))
+tree.left.right.set_right(Node(50))
+tree.set_right(Node(78))
+tree.right.set_right(Node(80))
+
+
+# Complexity: Theta(n)
+def in_order_walk(t):
+  if t is not None:
+    in_order_walk(t.left)
+    print(t.key, end=' ')
+    in_order_walk(t.right)
+
+
+# Complexity: Theta(n)
+def reverse_walk(t):
+  if t is not None:
+    reverse_walk(t.right)
+    print(t.key, end=' ')
+    reverse_walk(t.left)
+
+
+# Complexity (worst): Theta(n)
+def search(tree, k):
+  pass
+
+
+# Complexity (worst): Theta(n)
+def min(t):
+  if t is None:
+    return None
+  while t.left is not None:
+    t = t.left
+  return t
+
+
+# Complexity (worst): Theta(n)
+def max(t):
+  if t is None:
+    return None
+  while t.right is not None:
+    t = t.right
+  return t
+
+
+def successor(t):
+  if t.right is not None:
+    return min(t.right)
+  while t.parent is not None:
+    if t.parent.left == t:
+      return t.parent
+    else:
+      t = t.parent
+  return None
+
+
+def predecessor(t):
+  if t.left is not None:
+    return max(t.left)
+  while t is not None:
+    if t.parent.right == t:
+      return t.parent
+    else:
+      t = t.parent
+  return None
+
+
+def insert(t, k):
+  if t is None:
+    return Node(k)
+  if t.key < t.key:
+    t.set_left(insert(t.left, k))
+  else:
+    tree.set_right(insert(t.right, k))
+  return t
+
+def right_rotate(x):
+  # assume x is not None
+  # assume x.left is not None
+  t = x.left
+  x.left = t.right
+  t.right = x
+  return t
+
+def left_rotate(x):
+  # assume x is not None
+  # assume x.right is not None
+  t = x.right
+  x.right = t.left
+  t.left = x
+  return t
+
+def root_insert(t, k):
+  if t is None:
+    return Node(k)
+  if k > t.key:
+    t.set_right(root_insert(t.right, k))
+    return left_rotate(t)
+  else:
+    t.set_left(root_insert(t.left, k))
+    return right_rotate(t)
+
+###############################################################################
+# Code for printing trees, ignore this
+
+
+class Canvas:
+  def __init__(self, width):
+    self.line_width = width
+    self.canvas = []
+
+  def put_char(self, x, y, c):
+    if x < self.line_width:
+      pos = y * self.line_width + x
+      l = len(self.canvas)
+      if pos < l:
+        self.canvas[pos] = c
+      else:
+        self.canvas[l:] = [' '] * (pos - l)
+        self.canvas.append(c)
+
+  def print_out(self):
+    i = 0
+    for c in self.canvas:
+      sys.stdout.write(c)
+      i = i + 1
+      if i % self.line_width == 0:
+        sys.stdout.write('\n')
+    if i % self.line_width != 0:
+      sys.stdout.write('\n')
+
+
+def print_binary_r(t, x, y, canvas):
+  max_y = y
+  if t.left is not None:
+    x, max_y, lx, rx = print_binary_r(t.left, x, y + 2, canvas)
+    x = x + 1
+    for i in range(rx, x):
+      canvas.put_char(i, y + 1, '/')
+
+  middle_l = x
+  for c in str(t.key):
+    canvas.put_char(x, y, c)
+    x = x + 1
+  middle_r = x
+
+  if t.right is not None:
+    canvas.put_char(x, y + 1, '\\')
+    x = x + 1
+    x0, max_y2, lx, rx = print_binary_r(t.right, x, y + 2, canvas)
+    if max_y2 > max_y:
+      max_y = max_y2
+    for i in range(x, lx):
+      canvas.put_char(i, y + 1, '\\')
+    x = x0
+
+  return (x, max_y, middle_l, middle_r)
+
+
+def print_tree(t):
+  print_w(t, 80)
+
+
+def print_w(t, width):
+  canvas = Canvas(width)
+  print_binary_r(t, 0, 0, canvas)
+  canvas.print_out()
+
+###############################################################################
+
+
+if __name__ == "__main__":
+  print_tree(tree)
+
+  in_order_walk(tree)
+  print()
+
+  reverse_walk(tree)
+  print()
+
+  print(tree.left.right.right.key)
+  print(successor(tree.left.right.right).key)
+  print(predecessor(tree.left.right.right).key)
+