diff --git a/book/book_second_edition.pdf b/book/book_second_edition.pdf
index c52833d..e734a79 100644
Binary files a/book/book_second_edition.pdf and b/book/book_second_edition.pdf differ
diff --git a/src/programming_paradigms/oop/do_benchmark.py b/src/programming_paradigms/modules/do_benchmark.py
similarity index 100%
rename from src/programming_paradigms/oop/do_benchmark.py
rename to src/programming_paradigms/modules/do_benchmark.py
diff --git a/src/programming_paradigms/oop/HashTable.py b/src/programming_paradigms/oop/HashTable.py
deleted file mode 100644
index 073b4b1..0000000
--- a/src/programming_paradigms/oop/HashTable.py
+++ /dev/null
@@ -1,81 +0,0 @@
-#!/usr/bin/python3
-# mari von steinkirch @2013
-# steinkirch at gmail
-
-
-class HashTable:
-    ''' HashTable class that implements the Map abstract data type with 2 lists'''
-    def __init__(self):
-        self.size = 11
-        self.slots = [None] * self.size
-        self.data = [None] * self.size
-
-    def put(self,key,data):
-        hashvalue = self.hashfunction(key,len(self.slots))
-
-        if self.slots[hashvalue] == None:
-            self.slots[hashvalue] = key
-            self.data[hashvalue] = data
-        else:
-            if self.slots[hashvalue] == key:
-                self.data[hashvalue] = data  
-            else:
-                nextslot = self.rehash(hashvalue,len(self.slots))
-                while self.slots[nextslot] != None and \
-                      self.slots[nextslot] != key:
-                    nextslot = self.rehash(nextslot,len(self.slots))
-
-                if self.slots[nextslot] == None:
-                    self.slots[nextslot]=key
-                    self.data[nextslot]=data
-                else:
-                    self.data[nextslot] = data 
-
-    def hashfunction(self,key,size):
-        return key%size
-
-    def rehash(self,oldhash,size):
-        return (oldhash+1)%size
-
-    def get(self,key):
-        startslot = self.hashfunction(key,len(self.slots))
-
-        data = None
-        stop = False
-        found = False
-        position = startslot
-        while self.slots[position] != None and  \
-                       not found and not stop:
-            if self.slots[position] == key:
-                found = True
-                data = self.data[position]
-            else:
-                position=self.rehash(position,len(self.slots))
-                if position == startslot:
-                    stop = True
-        return data
-
-
-    def __getitem__(self,key):
-        return self.get(key)
-
-    def __setitem__(self,key,data):
-        self.put(key,data)      
-
-
-
-def test_HashTable(module_name='this module'):
-    H = HashTable()
-    H[54]="buffy"
-    H[26]="xander"
-    H[17]="giles"
-    print(H.slots)
-    print(H.data)
-        
-    s = 'Tests in {name} have {con}!'
-    print(s.format(name=module_name, con='passed'))
-
-
-if __name__ == '__main__':
-    test_HashTable()
-
diff --git a/src/trees/binary_tree.py b/src/trees/binary_tree.py
index fc33a52..31f0102 100644
--- a/src/trees/binary_tree.py
+++ b/src/trees/binary_tree.py
@@ -46,7 +46,7 @@ class NodeBT(object):
             self.right = new_node
         else:
             self.left = self.left._addNextNode(value, level_here+1)
-        return self
+        return self ## this is important, because the node return to the main
 
 
     def _searchForNode(self, value):
@@ -99,19 +99,26 @@ class NodeBT(object):
             elif not self.right and self.left:
                  return  self.left._isBalanced()
 
-    def _isBST(self):
+    def _isBST(self, mintree=None, maxtree=None):
         ''' Find whether the tree is a BST, inorder '''
         if self.item:
+            if not mintree:
+                mintree = self.item
+            if not maxtree:
+                maxtree = self.item
+
             if self._isLeaf():
                 return True
             elif self.left:
-                if self.left.item < self.item:
-                    return self.left._isBST()
+                if self.left.item < self.item and mintree > self.left.item:
+                    mintree = self.left.item
+                    return self.left._isBST(mintree, maxtree)
                 else:
                     return False
             elif self.right:
-                if self.right.item > self.item:
-                    return self.right._isBST()
+                if self.right.item > self.item and maxtree < self.right.item:
+                    maxtree = self.right.item
+                    return self.right._isBST(mintree, maxtree)
                 else:
                     return False
         else:
@@ -121,6 +128,9 @@ class NodeBT(object):
 
 
 
+
+
+
 class BinaryTree(object):
 
     def __init__(self):
@@ -141,6 +151,7 @@ class BinaryTree(object):
         else:
             print "Node not found."
 
+
     def getNodeLevel(self, item):
         node = self.root._searchForNode(item)
         if node:
@@ -148,19 +159,37 @@ class BinaryTree(object):
         else:
             print('Node not found')
 
+
     def isRoot(self, value):
         return self.root.item == value
 
+
     def getHeight(self):
         return self.root._getMaxHeight()
 
+
     def isBalanced(self):
         return self.root._isBalanced()
 
+
     def isBST(self):
         return self.root._isBST()
 
 
+    def preorder(self):
+        current = self.root
+        nodes, stack = [], []
+        while stack or current:
+            if current:
+                nodes.append(current.item) # thats what change
+                stack.append(current)
+                current = current.left
+            else:
+                current = stack.pop()
+                current = current.right
+        return nodes
+
+
 
 if __name__ == '__main__':
     bt = BinaryTree()
@@ -173,4 +202,5 @@ if __name__ == '__main__':
     print "Is node 1 a root? ", bt.isRoot(1)
     print "Whats the tree height? ", bt.getHeight()
     print "Is this tree BST? ", bt.isBST()
-    print "Is this tree balanced? ", bt.isBalanced()
\ No newline at end of file
+    print "Is this tree balanced? ", bt.isBalanced()
+    print (bt.preorder())
\ No newline at end of file
diff --git a/src/trees/transversal_BST_ancestor.py b/src/trees/transversal_BST_ancestor.py
index 51288cf..9be8c92 100644
--- a/src/trees/transversal_BST_ancestor.py
+++ b/src/trees/transversal_BST_ancestor.py
@@ -24,6 +24,8 @@ def find_ancestor(path, low_value, high_value):
                 return current_value
         elif low_value <= current_value <= high_value:
             return current_value
+        else:
+            return None # this is probably never touched