diff --git a/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb b/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
index 20f76bc..6db49ed 100644
--- a/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
+++ b/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:d6f2ef62f297b01c2d33ebe34af91db1e402323086d1abc1c6827557351df297"
+  "signature": "sha256:29a120258e2d108ed5eace08e071ad866ae379b4f24fde804401ee858a2090fb"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -988,6 +988,68 @@
       "If we try to extend the list via `+=` *\"then the statement executes STORE_SUBSCR, which calls the C function PyObject_SetItem, which checks if the object supports item assignment. In our case the object is a tuple, so PyObject_SetItem throws the TypeError. Mystery solved.\"*"
      ]
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "#### One more note about the `immutable` status of tuples. Tuples are famous for being immutable. However, how comes that this code works?"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "my_tup = (1,)\n",
+      "my_tup += (4,)\n",
+      "my_tup = my_tup + (5,)\n",
+      "print(my_tup)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "(1, 4, 5)\n"
+       ]
+      }
+     ],
+     "prompt_number": 6
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "What happens \"behind\" the curtains is that the tuple is not modified, but every time a new object is generated, which will inherit the old \"name tag\":"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "my_tup = (1,)\n",
+      "print(id(my_tup))\n",
+      "my_tup += (4,)\n",
+      "print(id(my_tup))\n",
+      "my_tup = my_tup + (5,)\n",
+      "print(id(my_tup))"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "4337381840\n",
+        "4357415496\n",
+        "4357289952\n"
+       ]
+      }
+     ],
+     "prompt_number": 8
+    },
     {
      "cell_type": "markdown",
      "metadata": {},
diff --git a/not_so_obvious_python_stuff.ipynb b/not_so_obvious_python_stuff.ipynb
index 20f76bc..6db49ed 100644
--- a/not_so_obvious_python_stuff.ipynb
+++ b/not_so_obvious_python_stuff.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:d6f2ef62f297b01c2d33ebe34af91db1e402323086d1abc1c6827557351df297"
+  "signature": "sha256:29a120258e2d108ed5eace08e071ad866ae379b4f24fde804401ee858a2090fb"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -988,6 +988,68 @@
       "If we try to extend the list via `+=` *\"then the statement executes STORE_SUBSCR, which calls the C function PyObject_SetItem, which checks if the object supports item assignment. In our case the object is a tuple, so PyObject_SetItem throws the TypeError. Mystery solved.\"*"
      ]
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "#### One more note about the `immutable` status of tuples. Tuples are famous for being immutable. However, how comes that this code works?"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "my_tup = (1,)\n",
+      "my_tup += (4,)\n",
+      "my_tup = my_tup + (5,)\n",
+      "print(my_tup)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "(1, 4, 5)\n"
+       ]
+      }
+     ],
+     "prompt_number": 6
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "What happens \"behind\" the curtains is that the tuple is not modified, but every time a new object is generated, which will inherit the old \"name tag\":"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "my_tup = (1,)\n",
+      "print(id(my_tup))\n",
+      "my_tup += (4,)\n",
+      "print(id(my_tup))\n",
+      "my_tup = my_tup + (5,)\n",
+      "print(id(my_tup))"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "4337381840\n",
+        "4357415496\n",
+        "4357289952\n"
+       ]
+      }
+     ],
+     "prompt_number": 8
+    },
     {
      "cell_type": "markdown",
      "metadata": {},