diff --git a/notebooks/Ch14-OOP.ipynb b/notebooks/Ch14-OOP.ipynb
index e3d52da..55f7216 100644
--- a/notebooks/Ch14-OOP.ipynb
+++ b/notebooks/Ch14-OOP.ipynb
@@ -57,7 +57,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -67,37 +67,18 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "data": {
-      "text/plain": [
-       "<__main__.Point at 0x7ff0f8815820>"
-      ]
-     },
-     "execution_count": 4,
-     "metadata": {},
-     "output_type": "execute_result"
-    }
-   ],
+   "outputs": [],
    "source": [
-    "a"
+    "type(a)"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "0 0\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "a.x = 0 # dynamically attach attriutes\n",
     "a.y = 0\n",
@@ -106,7 +87,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -115,21 +96,9 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "ename": "AttributeError",
-     "evalue": "'Point' object has no attribute 'x'",
-     "output_type": "error",
-     "traceback": [
-      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
-      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
-      "\u001b[0;32m/var/folders/4f/1pkkv7h960j42p0ppgk9n4ywjr6t_b/T/ipykernel_45410/1440403333.py\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mb\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mx\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
-      "\u001b[0;31mAttributeError\u001b[0m: 'Point' object has no attribute 'x'"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "b.x"
    ]
@@ -144,7 +113,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -170,6 +139,15 @@
     "        Point.count -= 1"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "print(Point.count)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -187,7 +165,69 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "a = Point()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "print(a.x, a.y)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "b = Point(10, 10)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "print(b.x, b.y)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "Point.count"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 46,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "<__main__.Point object at 0x7f850fddcfa0>\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(a)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 36,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -197,7 +237,7 @@
     "    # what is the access specifier for attributes?\n",
     "    print('p: x = {} and y = {}'.format(p.x, p.y))\n",
     "    print(\"Total point objects = {}\".format(Point.count)) # access class variable outside class\n",
-    "    #p.__del__() # call destructor explictly\n",
+    "    p.__del__() # call destructor explictly\n",
     "    p1 = Point(10, 100)\n",
     "    print(\"p1: x = {} and y = {}\".format(p1.x, p1.y))\n",
     "    print(\"Total point objects = {}\".format(Point.count))\n",
@@ -208,7 +248,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": 34,
    "metadata": {},
    "outputs": [
     {
@@ -216,26 +256,26 @@
      "output_type": "stream",
      "text": [
       "p: x = 0 and y = 0\n",
-      "Total point objects = 1\n",
+      "Total point objects = 3\n",
       "p1: x = 10 and y = 100\n",
-      "Total point objects = 2\n"
+      "Total point objects = 4\n"
      ]
     }
    ],
    "source": [
-    "someFunction()\n"
+    "someFunction()"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": 37,
    "metadata": {},
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Total point objects = 0\n"
+      "Total point objects = 2\n"
      ]
     }
    ],
@@ -245,7 +285,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 9,
+   "execution_count": 38,
    "metadata": {},
    "outputs": [
     {
@@ -253,9 +293,9 @@
      "output_type": "stream",
      "text": [
       "p: x = 0 and y = 0\n",
-      "Total point objects = 1\n",
+      "Total point objects = 3\n",
       "p1: x = 10 and y = 100\n",
-      "Total point objects = 2\n"
+      "Total point objects = 4\n"
      ]
     }
    ],
@@ -272,14 +312,14 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 10,
+   "execution_count": 39,
    "metadata": {},
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "<__main__.Point object at 0x7f94e48e3730> <__main__.Point object at 0x7f94e48e3820>\n"
+      "<__main__.Point object at 0x7f850fe356c0> <__main__.Point object at 0x7f850fe097b0>\n"
      ]
     }
    ],
@@ -310,7 +350,36 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": 40,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def dist_from_origin(self):\n",
+    "    import math\n",
+    "    dist = math.sqrt(self.x**2+self.y**2)\n",
+    "    return dist"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 41,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "100.4987562112089\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(dist_from_origin(p1))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 63,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -332,7 +401,7 @@
     "        return dist\n",
     "    \n",
     "    def __str__(self):\n",
-    "        return \"({}, {})\".format(self.x, self.y)\n",
+    "        return f\"({self.x}, {self.y})\"\n",
     "    \n",
     "    # destructor \n",
     "    def __del__(self):\n",
@@ -341,7 +410,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 12,
+   "execution_count": 64,
    "metadata": {},
    "outputs": [
     {
@@ -359,7 +428,36 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 13,
+   "execution_count": 65,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "p2 = Point(10, 200)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 66,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "200.24984394500785"
+      ]
+     },
+     "execution_count": 66,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "p2.dist_from_origin()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 62,
    "metadata": {},
    "outputs": [
     {
@@ -385,18 +483,9 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 15,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "(3, 2)\n",
-      "(sasf, 10)\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "p2 = Point(3, 2)\n",
     "print(p2)\n",
@@ -410,18 +499,19 @@
    "metadata": {},
    "source": [
     "### better approach to change state/attribute is via methods\n",
+    "\n",
     "- move(xx, yy) method is added to class to set new x and y values for a point objects\n",
     "\n",
     "### Member access specifiers\n",
+    "\n",
     "- Python doesn't support `private`, `public`, `protected` specifiers provided by C++, Java, etc.\n",
     "- all the members are public by default\n",
-    "- however, it uses `__` double leading underscore notation to treat members as private\n",
-    "    - this, however is not enforced"
+    "- however, you can use leading single `_` and double `__` underscores \"convention\" to treat members as private "
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 16,
+   "execution_count": 10,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -429,60 +519,67 @@
     "    \"\"\"\n",
     "    Point class represents and manipulates x and y coordinates\n",
     "    \"\"\"\n",
-    "    count = 0\n",
     "    \n",
     "    def __init__(self, xx=0, yy=0):\n",
     "        \"\"\"Create a new point with given x and y coords\"\"\"\n",
-    "        self.x = xx\n",
-    "        self.y = yy\n",
-    "        Point.count += 1\n",
+    "        \"\"\"_x and _y are protected method\"\"\"\n",
+    "        \n",
+    "        self._x = xx\n",
+    "        self._y = yy\n",
     "        \n",
     "    def dist_from_origin(self):\n",
     "        import math\n",
-    "        dist = math.sqrt(self.x**2+self.y**2)\n",
+    "        dist = math.sqrt(self._x**2+self._y**2)\n",
     "        return dist\n",
     "    \n",
     "    def __str__(self): # string representation of the class; useful in printing objects\n",
-    "        return \"({}, {})\".format(self.x, self.y)\n",
+    "        return f\"({self._x}, {self._y})\"\n",
+    "    \n",
+    "    # define getter method to get x\n",
+    "    def getX(self):\n",
+    "        if not self._x:\n",
+    "            return 0\n",
+    "        return self._x\n",
+    "    \n",
+    "    # better syntax\n",
+    "    @property\n",
+    "    def x(self):\n",
+    "        return self._x\n",
     "    \n",
     "    # use setters to set attributes\n",
     "    def setX(self, xx):\n",
     "        if isinstance(xx, int) or isinstance(xx, float):\n",
-    "            self.x = int(xx)\n",
+    "            self._x = int(xx)\n",
     "        elif isinstance(xx, str):\n",
     "            if xx.isnumeric():\n",
-    "                self.x = int(xx)\n",
+    "                self._x = int(xx)\n",
     "                \n",
-    "    def setY(self, yy):\n",
+    "    # better syntax for setter\n",
+    "    @x.setter\n",
+    "    def x(self, xx: int):\n",
+    "        self.setX(xx)\n",
+    "        \n",
+    "    @property\n",
+    "    def y(self):\n",
+    "        return self._y\n",
+    "        \n",
+    "    @y.setter\n",
+    "    def y(self, yy: int):\n",
     "        if isinstance(yy, int) or isinstance(yy, float):\n",
-    "            self.y = int(yy)\n",
+    "            self._y = int(yy)\n",
     "        elif isinstance(yy, str):\n",
     "            if yy.isnumeric():\n",
-    "                self.y = int(yy)\n",
-    "             \n",
-    "    # use getters to get attributes\n",
-    "    def getX(self):\n",
-    "        if not self.x:\n",
-    "            return 0\n",
-    "        return self.x\n",
-    "    \n",
-    "    def getY(self):\n",
-    "        return self.y\n",
+    "                self._y = int(yy)\n",
+    "\n",
     "    \n",
     "    def move(self, xx, yy):\n",
-    "        self.setX(xx)\n",
-    "        self.setY(yy)\n",
-    "        #self.x = xx\n",
-    "        #self.y = yy\n",
-    "        \n",
-    "    # destructor\n",
-    "    def __del__(self):\n",
-    "        Point.count -= 1"
+    "        self.x = xx\n",
+    "        self.y = yy"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 11,
    "metadata": {},
    "outputs": [
     {
@@ -503,7 +600,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 18,
+   "execution_count": 12,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -512,7 +609,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 20,
+   "execution_count": 13,
    "metadata": {},
    "outputs": [
     {
@@ -531,23 +628,142 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## sameness - alias or deep copy"
+    "## Operator Overloading\n",
+    "\n",
+    "- https://docs.python.org/3/reference/datamodel.html\n",
+    "- Python lets you overload special operators (e.g., +, -, /, //, %, etc.) for your class\n",
+    "- Goal is to make your class as easy and seamless to use as possible\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 23,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "class Point:\n",
+    "    \"\"\"\n",
+    "    Point class represents and manipulates x and y coordinates\n",
+    "    \"\"\"\n",
+    "    \n",
+    "    def __init__(self, xx=0, yy=0):\n",
+    "        \"\"\"Create a new point with given x and y coords\"\"\"\n",
+    "        \"\"\"_x and _y are protected method\"\"\"\n",
+    "        \n",
+    "        self._x = xx\n",
+    "        self._y = yy\n",
+    "        \n",
+    "    def dist_from_origin(self):\n",
+    "        import math\n",
+    "        dist = math.sqrt(self._x**2+self._y**2)\n",
+    "        return dist\n",
+    "    \n",
+    "    def __str__(self): # string representation of the class; useful in printing objects\n",
+    "        return f\"({self._x}, {self._y})\"\n",
+    "    \n",
+    "    @property\n",
+    "    def x(self):\n",
+    "        if not self._x:\n",
+    "            return 0\n",
+    "        return self._x\n",
+    "    \n",
+    "    @x.setter\n",
+    "    def x(self, xx: int):\n",
+    "        if isinstance(xx, int) or isinstance(xx, float):\n",
+    "            self._x = int(xx)\n",
+    "        elif isinstance(xx, str):\n",
+    "            if xx.isnumeric():\n",
+    "                self._x = int(xx)\n",
+    "        \n",
+    "    @property\n",
+    "    def y(self):\n",
+    "        return self._y\n",
+    "        \n",
+    "    @y.setter\n",
+    "    def y(self, yy: int):\n",
+    "        if isinstance(yy, int) or isinstance(yy, float):\n",
+    "            self._y = int(yy)\n",
+    "        elif isinstance(yy, str):\n",
+    "            if yy.isnumeric():\n",
+    "                self._y = int(yy)\n",
+    "\n",
+    "    \n",
+    "    def move(self, xx, yy):\n",
+    "        self.x = xx\n",
+    "        \n",
+    "    def __add__(self, other: \"Point\"):\n",
+    "        \"\"\"Overload + operator\"\"\"\n",
+    "        new_x = self.x + other.x\n",
+    "        new_y = self.y + other.y\n",
+    "        return Point(new_x, new_y)\n",
+    "    \n",
+    "    \n",
+    "    def __eq__(self, other: \"Point\"):\n",
+    "        return self.x == other.x and self.y == other.y"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 21,
+   "execution_count": 22,
    "metadata": {},
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "True\n",
-      "False\n"
+      "(5, 9)\n"
      ]
     }
    ],
+   "source": [
+    "p1 = Point(2, 4)\n",
+    "p2 = Point(3, 5)\n",
+    "p3 = p1+p2\n",
+    "print(p3)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 24,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "assert p1 != p2"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 25,
+   "metadata": {},
+   "outputs": [
+    {
+     "ename": "AssertionError",
+     "evalue": "",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[0;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
+      "Cell \u001b[0;32mIn[25], line 1\u001b[0m\n\u001b[0;32m----> 1\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m p1 \u001b[38;5;241m==\u001b[39m p2\n",
+      "\u001b[0;31mAssertionError\u001b[0m: "
+     ]
+    }
+   ],
+   "source": [
+    "assert p1 == p2"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## sameness - alias or deep copy"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
    "source": [
     "import copy\n",
     "p2 = Point(3, 4)\n",
@@ -566,11 +782,11 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 24,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
-    "def print_point(pt):\n",
+    "def print_point(pt: Point):\n",
     "    pt.x = 100\n",
     "    pt.y = 100\n",
     "    print(pt)"
@@ -578,21 +794,20 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 25,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "(100, 100)\n",
-      "(100, 100)\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "p = Point(10, 10)\n",
-    "print_point(p)\n",
+    "print_point(p)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
     "print(p)"
    ]
   },
@@ -615,7 +830,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 28,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -628,17 +843,9 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 29,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "(5, 5)\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "p = Point(4, 6)\n",
     "q = Point(6, 4)\n",
@@ -666,7 +873,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 30,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -685,18 +892,9 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 31,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "box:  ((0, 0), 100, 200)\n",
-      "bomb:  ((100, 80), 5, 10)\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "box = Rectangle(Point(0, 0), 100, 200)\n",
     "bomb = Rectangle(Point(100, 80), 5, 10)    # In my video game\n",
@@ -832,7 +1030,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 32,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -853,7 +1051,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 33,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -862,60 +1060,27 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 34,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "data": {
-      "text/plain": [
-       "('instance method called', <__main__.MyClass at 0x7f94e4901820>)"
-      ]
-     },
-     "execution_count": 34,
-     "metadata": {},
-     "output_type": "execute_result"
-    }
-   ],
+   "outputs": [],
    "source": [
     "c.method()"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 35,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "data": {
-      "text/plain": [
-       "('class method called', __main__.MyClass)"
-      ]
-     },
-     "execution_count": 35,
-     "metadata": {},
-     "output_type": "execute_result"
-    }
-   ],
+   "outputs": [],
    "source": [
     "MyClass.classmethod()"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 36,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "data": {
-      "text/plain": [
-       "'static method called'"
-      ]
-     },
-     "execution_count": 36,
-     "metadata": {},
-     "output_type": "execute_result"
-    }
-   ],
+   "outputs": [],
    "source": [
     "MyClass.staticmethod()"
    ]
@@ -981,13 +1146,6 @@
     "# because of exception due to invalid grades, class_grades_invalid object is never created\n",
     "print(class_grades_invalid.grades)"
    ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": []
   }
  ],
  "metadata": {
@@ -1006,7 +1164,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.9.7"
+   "version": "3.10.8"
   }
  },
  "nbformat": 4,