diff --git a/core/structs.ipynb b/core/structs.ipynb
index 3c24bb4..ca6e085 100644
--- a/core/structs.ipynb
+++ b/core/structs.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:81da7477f866f68f73a55003c5ea2e9a1ebc2c30bc7f6b884fa153c45265f794"
+  "signature": "sha256:c5099245c74de456735197b7914b9a407b7fd42bc3fd7db0d637d1423436d0e6"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -338,13 +338,13 @@
       {
        "metadata": {},
        "output_type": "pyout",
-       "prompt_number": 39,
+       "prompt_number": 12,
        "text": [
         "[1, 2, 3]"
        ]
       }
      ],
-     "prompt_number": 39
+     "prompt_number": 12
     },
     {
      "cell_type": "markdown",
@@ -1077,13 +1077,13 @@
       {
        "metadata": {},
        "output_type": "pyout",
-       "prompt_number": 51,
+       "prompt_number": 38,
        "text": [
         "[1, 2, 5, 7, 8, 9, (1, 2), (4, 2)]"
        ]
       }
      ],
-     "prompt_number": 51
+     "prompt_number": 38
     },
     {
      "cell_type": "markdown",
@@ -1111,13 +1111,51 @@
       {
        "metadata": {},
        "output_type": "pyout",
-       "prompt_number": 53,
+       "prompt_number": 39,
        "text": [
         "[(1, 2), (1, 2), (4, 2), 1, 5, 2, 9, 9, 7, 8, 1, 5, 2]"
        ]
       }
      ],
-     "prompt_number": 53
+     "prompt_number": 39
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "## enumerate"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "enumerate gives you the index of a collection and the value"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "numbers = ['zero', 'one', 'two', 'three']\n",
+      "for i, number in enumerate(numbers):\n",
+      "    print(i, number)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "(0, 'zero')\n",
+        "(1, 'one')\n",
+        "(2, 'two')\n",
+        "(3, 'three')\n"
+       ]
+      }
+     ],
+     "prompt_number": 40
     },
     {
      "cell_type": "markdown",
@@ -1210,7 +1248,7 @@
        ]
       }
      ],
-     "prompt_number": 50
+     "prompt_number": 43
     },
     {
      "cell_type": "markdown",
@@ -1233,13 +1271,13 @@
       {
        "metadata": {},
        "output_type": "pyout",
-       "prompt_number": 47,
+       "prompt_number": 44,
        "text": [
         "(1, 2, 3)"
        ]
       }
      ],
-     "prompt_number": 47
+     "prompt_number": 44
     },
     {
      "cell_type": "code",
@@ -1253,21 +1291,13 @@
       {
        "metadata": {},
        "output_type": "pyout",
-       "prompt_number": 48,
+       "prompt_number": 45,
        "text": [
         "('one', 'two', 'three')"
        ]
       }
      ],
-     "prompt_number": 48
-    },
-    {
-     "cell_type": "code",
-     "collapsed": false,
-     "input": [],
-     "language": "python",
-     "metadata": {},
-     "outputs": []
+     "prompt_number": 45
     }
    ],
    "metadata": {}