diff --git a/.ipynb_checkpoints/timeit_test-checkpoint.ipynb b/.ipynb_checkpoints/timeit_test-checkpoint.ipynb
index 8ac1b2f..1ea9000 100644
--- a/.ipynb_checkpoints/timeit_test-checkpoint.ipynb
+++ b/.ipynb_checkpoints/timeit_test-checkpoint.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:30bb811f79dc78fe63221c8960bb4237c811b94fdf197b6479709aff3244cb08"
+  "signature": "sha256:e6a1d9a637dfbad45211a98a5bbc35255dc8f168a834ed466c363dfc384c0f59"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -19,7 +19,31 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "### String formatting - `.format()` vs. `%s`"
+      "# Sections\n",
+      "- [String formatting](#string_formatting)\n",
+      "    - [String formatting - .format() vs. binary operator %s](#str_format_bin)\n",
+      "    - [String Reversing - [::-1] vs. `''.join(reversed())`](#str_reverse)\n",
+      "- [List Operations](#list_operations)\n",
+      "    - [List Reversing - [::-1] vs. reverse() vs. reversed()](#list_reverse)\n",
+      "- [Dictionary Operations](#dict_ops) \n",
+      "    - [Adding elements to a dictionary](#adding_dict_elements)"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='string_formatting'></a>\n",
+      "\n",
+      "# String formatting"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='str_format_bin'></a>\n",
+      "### String formatting - `.format()` vs. binary operator `%s`"
      ]
     },
     {
@@ -74,6 +98,7 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
+      "<a name='str_reverse'></a>\n",
       "### String Reversing - `[::-1]` vs. `''.join(reversed())`"
      ]
     },
@@ -129,6 +154,15 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
+      "<a name='list_operations'></a>\n",
+      "# List Operations"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='list_reverse'></a>\n",
       "### List Reversing - `[::-1]` vs. `reverse()` vs. `reversed()`"
      ]
     },
@@ -166,8 +200,8 @@
        "output_type": "stream",
        "stream": "stdout",
        "text": [
-        "1000000 loops, best of 3: 857 ns per loop\n",
-        "1000000 loops, best of 3: 1.78 \u00b5s per loop"
+        "1000000 loops, best of 3: 930 ns per loop\n",
+        "1000000 loops, best of 3: 1.89 \u00b5s per loop"
        ]
       },
       {
@@ -175,7 +209,7 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "1000000 loops, best of 3: 758 ns per loop"
+        "1000000 loops, best of 3: 775 ns per loop"
        ]
       },
       {
@@ -186,7 +220,96 @@
        ]
       }
      ],
-     "prompt_number": 10
+     "prompt_number": 1
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='dict_ops'></a>\n",
+      "# Dictionary Operations "
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='adding_dict_elements'></a>\n",
+      "## Adding elements to a Dictionary"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "import random\n",
+      "\n",
+      "random.seed(123)\n",
+      "rand_ints = [randrange(1, 10) for i in range(100)]\n",
+      "\n",
+      "def add_element_check1(my_dict, elements):\n",
+      "    for e in elements:\n",
+      "        if e not in my_dict:\n",
+      "            my_dict[e] = 1\n",
+      "        else:\n",
+      "            my_dict[e] += 1\n",
+      "            \n",
+      "def add_element_check2(my_dict, elements):\n",
+      "    for e in elements:\n",
+      "        if e not in my_dict:\n",
+      "            my_dict[e] = 0\n",
+      "        my_dict[e] += 1            \n",
+      "\n",
+      "def add_element_except(my_dict):\n",
+      "    for e in elements:\n",
+      "        try:\n",
+      "            elements[e] += 1\n",
+      "        except KeyError:\n",
+      "            elements[e] = 1\n",
+      "        "
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "1\n",
+        "5\n",
+        "2\n",
+        "7\n",
+        "5\n",
+        "2\n",
+        "1\n",
+        "7\n",
+        "9\n",
+        "9\n",
+        "\n",
+        "\n",
+        "6\n",
+        "6\n",
+        "1\n",
+        "3\n",
+        "3\n",
+        "6\n",
+        "9\n",
+        "6\n",
+        "4\n",
+        "3\n"
+       ]
+      }
+     ],
+     "prompt_number": 16
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 15
     },
     {
      "cell_type": "code",
diff --git a/timeit_test.ipynb b/timeit_test.ipynb
index 8ac1b2f..7cb8318 100644
--- a/timeit_test.ipynb
+++ b/timeit_test.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:30bb811f79dc78fe63221c8960bb4237c811b94fdf197b6479709aff3244cb08"
+  "signature": "sha256:629f08ba90badbccee0e3581db0e76c716d0b93abc92869d2dc5176ac6b02854"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -19,7 +19,31 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "### String formatting - `.format()` vs. `%s`"
+      "# Sections\n",
+      "- [String formatting](#string_formatting)\n",
+      "    - [String formatting - .format() vs. binary operator %s](#str_format_bin)\n",
+      "    - [String Reversing - [::-1] vs. `''.join(reversed())`](#str_reverse)\n",
+      "- [List Operations](#list_operations)\n",
+      "    - [List Reversing - [::-1] vs. reverse() vs. reversed()](#list_reverse)\n",
+      "- [Dictionary Operations](#dict_ops) \n",
+      "    - [Adding elements to a dictionary](#adding_dict_elements)"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='string_formatting'></a>\n",
+      "\n",
+      "# String formatting"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='str_format_bin'></a>\n",
+      "### String formatting - `.format()` vs. binary operator `%s`"
      ]
     },
     {
@@ -74,6 +98,7 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
+      "<a name='str_reverse'></a>\n",
       "### String Reversing - `[::-1]` vs. `''.join(reversed())`"
      ]
     },
@@ -129,6 +154,15 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
+      "<a name='list_operations'></a>\n",
+      "# List Operations"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='list_reverse'></a>\n",
       "### List Reversing - `[::-1]` vs. `reverse()` vs. `reversed()`"
      ]
     },
@@ -166,8 +200,8 @@
        "output_type": "stream",
        "stream": "stdout",
        "text": [
-        "1000000 loops, best of 3: 857 ns per loop\n",
-        "1000000 loops, best of 3: 1.78 \u00b5s per loop"
+        "1000000 loops, best of 3: 930 ns per loop\n",
+        "1000000 loops, best of 3: 1.89 \u00b5s per loop"
        ]
       },
       {
@@ -175,7 +209,7 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "1000000 loops, best of 3: 758 ns per loop"
+        "1000000 loops, best of 3: 775 ns per loop"
        ]
       },
       {
@@ -186,7 +220,186 @@
        ]
       }
      ],
-     "prompt_number": 10
+     "prompt_number": 1
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='dict_ops'></a>\n",
+      "# Dictionary Operations "
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<a name='adding_dict_elements'></a>\n",
+      "## Adding elements to a Dictionary\n",
+      "\n",
+      "All three functions below count how often different elements (values) occur in a list.  \n",
+      "E.g., for the list ['a', 'b', 'a', 'c'], the dictionary would look like this:  \n",
+      "`my_dict = {'a': 2, 'b': 1, 'c': 1}`"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "import random\n",
+      "import copy\n",
+      "import timeit\n",
+      "\n",
+      "\n",
+      "\n",
+      "def add_element_check1(my_dict, elements):\n",
+      "    for e in elements:\n",
+      "        if e not in my_dict:\n",
+      "            my_dict[e] = 1\n",
+      "        else:\n",
+      "            my_dict[e] += 1\n",
+      "            \n",
+      "def add_element_check2(my_dict, elements):\n",
+      "    for e in elements:\n",
+      "        if e not in my_dict:\n",
+      "            my_dict[e] = 0\n",
+      "        my_dict[e] += 1            \n",
+      "\n",
+      "def add_element_except(my_dict, elements):\n",
+      "    for e in elements:\n",
+      "        try:\n",
+      "            my_dict[e] += 1\n",
+      "        except KeyError:\n",
+      "            my_dict[e] = 1\n",
+      "            \n",
+      "\n",
+      "random.seed(123)\n",
+      "rand_ints = [randrange(1, 10) for i in range(100)]\n",
+      "empty_dict = {}\n",
+      "\n",
+      "print('Results for 100 integers in range 1-10') \n",
+      "%timeit add_element_check1(copy.deepcopy(empty_dict), rand_ints)\n",
+      "%timeit add_element_check2(copy.deepcopy(empty_dict), rand_ints)\n",
+      "%timeit add_element_except(copy.deepcopy(empty_dict), rand_ints)\n",
+      "            \n",
+      "print('\\nResults for 1000 integers in range 1-10')            \n",
+      "rand_ints = [randrange(1, 10) for i in range(1000)]\n",
+      "empty_dict = {}\n",
+      "\n",
+      "%timeit add_element_check1(copy.deepcopy(empty_dict), rand_ints)\n",
+      "%timeit add_element_check2(copy.deepcopy(empty_dict), rand_ints)\n",
+      "%timeit add_element_except(copy.deepcopy(empty_dict), rand_ints)\n",
+      "\n",
+      "print('\\nResults for 1000 integers in range 1-1000')            \n",
+      "rand_ints = [randrange(1, 10) for i in range(1000)]\n",
+      "empty_dict = {}\n",
+      "\n",
+      "%timeit add_element_check1(copy.deepcopy(empty_dict), rand_ints)\n",
+      "%timeit add_element_check2(copy.deepcopy(empty_dict), rand_ints)\n",
+      "%timeit add_element_except(copy.deepcopy(empty_dict), rand_ints)\n",
+      "\n",
+      "# Python 3.4.0\n",
+      "# MacOS X 10.9.2\n",
+      "# 2.4 GHz Intel Core Duo\n",
+      "# 8 GB 1067 Mhz DDR3\n",
+      "#"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "Results for 100 integers in range 1-10\n",
+        "10000 loops, best of 3: 30.5 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "10000 loops, best of 3: 32.4 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "10000 loops, best of 3: 31.7 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "\n",
+        "Results for 1000 integers in range 1-10\n",
+        "1000 loops, best of 3: 241 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "1000 loops, best of 3: 247 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "1000 loops, best of 3: 209 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "\n",
+        "Results for 1000 integers in range 1-1000\n",
+        "1000 loops, best of 3: 241 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "1000 loops, best of 3: 247 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "1000 loops, best of 3: 206 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n"
+       ]
+      }
+     ],
+     "prompt_number": 25
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "### Conclusion\n",
+      "Interestingly, the `try-except` loop pays off if we have more elements (here: 1000 integers instead of 100) as dictionary keys to check. Also, it doesn't matter much whether the elements exist or do not exist in the dictionary, yet."
+     ]
     },
     {
      "cell_type": "code",