diff --git a/002-basic-control-structures/Basic control structures II.ipynb b/002-basic-control-structures/Basic control structures II.ipynb
index f8b129e..303f131 100644
--- a/002-basic-control-structures/Basic control structures II.ipynb	
+++ b/002-basic-control-structures/Basic control structures II.ipynb	
@@ -2212,7 +2212,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 1,
    "metadata": {
     "hideCode": false,
     "hidePrompt": false
@@ -2235,12 +2235,187 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
-   "metadata": {
-    "hideCode": false,
-    "hidePrompt": false
-   },
-   "outputs": [],
+   "execution_count": 4,
+   "metadata": {
+    "hideCode": false,
+    "hidePrompt": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "2\n",
+      "3\n",
+      "5\n",
+      "7\n",
+      "11\n",
+      "13\n",
+      "17\n",
+      "19\n",
+      "23\n",
+      "29\n",
+      "31\n",
+      "37\n",
+      "41\n",
+      "43\n",
+      "47\n",
+      "53\n",
+      "59\n",
+      "61\n",
+      "67\n",
+      "71\n",
+      "73\n",
+      "79\n",
+      "83\n",
+      "89\n",
+      "97\n",
+      "101\n",
+      "103\n",
+      "107\n",
+      "109\n",
+      "113\n",
+      "127\n",
+      "131\n",
+      "137\n",
+      "139\n",
+      "149\n",
+      "151\n",
+      "157\n",
+      "163\n",
+      "167\n",
+      "173\n",
+      "179\n",
+      "181\n",
+      "191\n",
+      "193\n",
+      "197\n",
+      "199\n",
+      "211\n",
+      "223\n",
+      "227\n",
+      "229\n",
+      "233\n",
+      "239\n",
+      "241\n",
+      "251\n",
+      "257\n",
+      "263\n",
+      "269\n",
+      "271\n",
+      "277\n",
+      "281\n",
+      "283\n",
+      "293\n",
+      "307\n",
+      "311\n",
+      "313\n",
+      "317\n",
+      "331\n",
+      "337\n",
+      "347\n",
+      "349\n",
+      "353\n",
+      "359\n",
+      "367\n",
+      "373\n",
+      "379\n",
+      "383\n",
+      "389\n",
+      "397\n",
+      "401\n",
+      "409\n",
+      "419\n",
+      "421\n",
+      "431\n",
+      "433\n",
+      "439\n",
+      "443\n",
+      "449\n",
+      "457\n",
+      "461\n",
+      "463\n",
+      "467\n",
+      "479\n",
+      "487\n",
+      "491\n",
+      "499\n",
+      "503\n",
+      "509\n",
+      "521\n",
+      "523\n",
+      "541\n",
+      "547\n",
+      "557\n",
+      "563\n",
+      "569\n",
+      "571\n",
+      "577\n",
+      "587\n",
+      "593\n",
+      "599\n",
+      "601\n",
+      "607\n",
+      "613\n",
+      "617\n",
+      "619\n",
+      "631\n",
+      "641\n",
+      "643\n",
+      "647\n",
+      "653\n",
+      "659\n",
+      "661\n",
+      "673\n",
+      "677\n",
+      "683\n",
+      "691\n",
+      "701\n",
+      "709\n",
+      "719\n",
+      "727\n",
+      "733\n",
+      "739\n",
+      "743\n",
+      "751\n",
+      "757\n",
+      "761\n",
+      "769\n",
+      "773\n",
+      "787\n",
+      "797\n",
+      "809\n",
+      "811\n",
+      "821\n",
+      "823\n",
+      "827\n",
+      "829\n",
+      "839\n",
+      "853\n",
+      "857\n",
+      "859\n",
+      "863\n",
+      "877\n",
+      "881\n",
+      "883\n",
+      "887\n",
+      "907\n",
+      "911\n",
+      "919\n",
+      "929\n",
+      "937\n",
+      "941\n",
+      "947\n",
+      "953\n",
+      "967\n",
+      "971\n",
+      "977\n",
+      "983\n",
+      "991\n",
+      "997\n"
+     ]
+    }
+   ],
    "source": [
     "# Print all the primes below 1000\n",
     "for prime in primes():\n",
@@ -2261,9 +2436,9 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 3,
    "metadata": {
-    "hideCode": true,
+    "hideCode": false,
     "hideOutput": false,
     "hidePrompt": false
    },
diff --git a/020-patterns/Solid Ideas.ipynb b/020-patterns/Solid Ideas.ipynb
index db7b6af..a13d514 100644
--- a/020-patterns/Solid Ideas.ipynb	
+++ b/020-patterns/Solid Ideas.ipynb	
@@ -377,7 +377,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 27,
+   "execution_count": 2,
    "metadata": {},
    "outputs": [
     {
@@ -387,7 +387,7 @@
      "traceback": [
       "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
       "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
-      "\u001b[0;32m<ipython-input-27-1dcee1546bf0>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      9\u001b[0m     \u001b[0;34m...\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     10\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 11\u001b[0;31m \u001b[0mDolfin\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[0;32m<ipython-input-2-1dcee1546bf0>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      9\u001b[0m     \u001b[0;34m...\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     10\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 11\u001b[0;31m \u001b[0mDolfin\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
       "\u001b[0;31mTypeError\u001b[0m: Can't instantiate abstract class Dolfin with abstract methods walk"
      ]
     }
@@ -406,6 +406,39 @@
     "Dolfin()"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "metadata": {},
+   "outputs": [
+    {
+     "ename": "NotImplementedError",
+     "evalue": "This animal cannot walk",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[0;31mNotImplementedError\u001b[0m                       Traceback (most recent call last)",
+      "\u001b[0;32m<ipython-input-7-7fc9b65d9980>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m     10\u001b[0m     \u001b[0;34m...\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     11\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 12\u001b[0;31m \u001b[0mDolfin\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mwalk\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[0;32m<ipython-input-7-7fc9b65d9980>\u001b[0m in \u001b[0;36mwalk\u001b[0;34m(self)\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;32mclass\u001b[0m \u001b[0mAnimal\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      2\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0mwalk\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 3\u001b[0;31m         \u001b[0;32mraise\u001b[0m \u001b[0mNotImplementedError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"This animal cannot walk\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      4\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m \u001b[0;32mclass\u001b[0m \u001b[0mMonkey\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mAnimal\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
+      "\u001b[0;31mNotImplementedError\u001b[0m: This animal cannot walk"
+     ]
+    }
+   ],
+   "source": [
+    "class Animal:\n",
+    "    def walk(self):\n",
+    "        raise NotImplementedError(\"This animal cannot walk\")\n",
+    "        \n",
+    "class Monkey(Animal):\n",
+    "    def walk(self):\n",
+    "        ...\n",
+    "        \n",
+    "class Dolfin(Animal):\n",
+    "    ...\n",
+    "    \n",
+    "Dolfin().walk()"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -436,7 +469,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 29,
+   "execution_count": 8,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -459,7 +492,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 30,
+   "execution_count": 9,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -629,10 +662,105 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 16,
    "metadata": {},
-   "outputs": [],
-   "source": []
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "['left-front',\n",
+       " 'left-middle-front',\n",
+       " 'left-middle-back',\n",
+       " 'left-back',\n",
+       " 'right-front',\n",
+       " 'right-middle-front',\n",
+       " 'right-middle-back',\n",
+       " 'right-back',\n",
+       " 'left-back',\n",
+       " 'right-back',\n",
+       " 'left-front',\n",
+       " 'right-front',\n",
+       " 'left-back',\n",
+       " 'right-back',\n",
+       " 'left-front',\n",
+       " 'right-front']"
+      ]
+     },
+     "execution_count": 16,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "class Animal:\n",
+    "    name = 'Unknown'\n",
+    "    \n",
+    "    # OCP: Even if our animal doesn't have legs, it will nonetheless have a legs\n",
+    "    # list, if this constructor gets called. If users of the Animal class use this\n",
+    "    # directly, they could get silent bugs by looking at e.g. dolphin.legs\n",
+    "    def __init__(self):\n",
+    "        self.legs = ['left-back', 'right-back', 'left-front', 'right-front']\n",
+    "        \n",
+    "    # ISP: not all animals have legs, why are we requiring them to have leg-names?\n",
+    "    @abc.abstractmethod\n",
+    "    def get_leg_names(self):\n",
+    "        pass\n",
+    "\n",
+    "class Giraffe(Animal):\n",
+    "    name = 'Giraffe'\n",
+    "    \n",
+    "    def get_leg_names(self):\n",
+    "        return ', '.join(self.legs)\n",
+    "    \n",
+    "class Tarantula(Animal):\n",
+    "    name = 'Tarantula'\n",
+    "    \n",
+    "    def __init__(self):\n",
+    "        self.legs = [\n",
+    "            'left-front', 'left-middle-front', 'left-middle-back', 'left-back',\n",
+    "            'right-front', 'right-middle-front', 'right-middle-back', 'right-back'\n",
+    "        ]\n",
+    "    \n",
+    "    def get_leg_names(self):\n",
+    "        return ', '.join(self.legs)\n",
+    "\n",
+    "class Butterfly(Animal):\n",
+    "    name = 'Butterfly'\n",
+    "    has_transformed = None\n",
+    "    \n",
+    "    # LSP: we are expecting this to initialize whether\n",
+    "    # our butterfly is still a caterpillar or not, but that's\n",
+    "    # not something that users of the superclass will do...\n",
+    "    def set_is_transformed(self, transformed):\n",
+    "        self.has_transformed = transformed\n",
+    "        \n",
+    "    def get_leg_names(self):\n",
+    "        return ['leg {n}' for n in range(6 if self.has_transformed else 16)]\n",
+    "\n",
+    "class Zoo:\n",
+    "    def __init__(self):\n",
+    "        # DIP: bit of an extreme example, but rather than saying which animals\n",
+    "        # are in our zoo, or passing a creator function, the constructor will\n",
+    "        # only ever work exactly with these three animals.\n",
+    "        self.animals = [\n",
+    "            Tarantula(),\n",
+    "            Butterfly(),\n",
+    "            Giraffe()\n",
+    "        ]\n",
+    "    \n",
+    "    # SRP: we are baking in how animals are shown to our domain model class\n",
+    "    # (might also notice this links to separation of layers in DDD/MVC)\n",
+    "    def print_animals():\n",
+    "        for animal in self.animals:\n",
+    "            print(f'A {animal.name} has {len(animal.get_leg_names())}')\n",
+    "            \n",
+    "zoo = Zoo()\n",
+    "\n",
+    "# LOD: not only are we baking in the assumption that animals have legs,\n",
+    "# we're baking in the way that's stored - note that this has gone wrong for\n",
+    "# Butterflies who do not use the legs list\n",
+    "sum((zoo.animals[i].legs for i in range(3)), [])"
+   ]
   }
  ],
  "metadata": {