diff --git a/code/03/data_structures.ipynb b/code/03/data_structures.ipynb
index be02f42..fb1181e 100644
--- a/code/03/data_structures.ipynb
+++ b/code/03/data_structures.ipynb
@@ -14,38 +14,46 @@
   },
   {
    "cell_type": "markdown",
-   "source": [
-    "## 创建列表"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%% md\n"
     }
-   }
+   },
+   "source": [
+    "## 创建列表"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 172,
-   "outputs": [],
-   "source": [
-    "# literal\n",
-    "numbers = [1, 2, 3, 4, 5]"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
+   },
+   "outputs": [],
+   "source": [
+    "# literal\n",
+    "numbers = [1, 2, 3, 4, 5]"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 173,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "list"
+      "text/plain": [
+       "list"
+      ]
      },
      "execution_count": 173,
      "metadata": {},
@@ -54,17 +62,17 @@
    ],
    "source": [
     "type(numbers)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 174,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 174,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -76,36 +84,38 @@
    ],
    "source": [
     "print(numbers)"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 175,
-   "outputs": [],
-   "source": [
-    "# key word\n",
-    "alphabet = list(\"abcde\")"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
+   },
+   "outputs": [],
+   "source": [
+    "# key word\n",
+    "alphabet = list(\"abcde\")"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 176,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "list"
+      "text/plain": [
+       "list"
+      ]
      },
      "execution_count": 176,
      "metadata": {},
@@ -113,18 +123,18 @@
     }
    ],
    "source": [
-    "type(numbers)  # list"
-   ],
+    "type(alphabet)  # list"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 177,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 177,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -136,29 +146,29 @@
    ],
    "source": [
     "print(alphabet)"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "markdown",
-   "source": [
-    "## 索引与切片"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%% md\n"
     }
-   }
+   },
+   "source": [
+    "## 索引与切片"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 178,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -171,21 +181,23 @@
    "source": [
     "idx = alphabet.index(\"c\")\n",
     "print(idx)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 179,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 179,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "'c'"
+      "text/plain": [
+       "'c'"
+      ]
      },
      "execution_count": 179,
      "metadata": {},
@@ -194,21 +206,23 @@
    ],
    "source": [
     "alphabet[idx]"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 180,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 180,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "[2, 3, 4]"
+      "text/plain": [
+       "[2, 3, 4]"
+      ]
      },
      "execution_count": 180,
      "metadata": {},
@@ -217,21 +231,23 @@
    ],
    "source": [
     "numbers[1:4]"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 181,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 181,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "[5]"
+      "text/plain": [
+       "[5]"
+      ]
      },
      "execution_count": 181,
      "metadata": {},
@@ -240,45 +256,45 @@
    ],
    "source": [
     "numbers[-1:]"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "markdown",
-   "source": [
-    "## 常用的列表方法"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%% md\n"
     }
-   }
+   },
+   "source": [
+    "## 常用的列表方法"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 182,
-   "outputs": [],
-   "source": [
-    "# append\n",
-    "others = [7, 8, 9]\n",
-    "numbers.append(others)"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
+   },
+   "outputs": [],
+   "source": [
+    "# append\n",
+    "others = [7, 8, 9]\n",
+    "numbers.append(others)"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 183,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -290,33 +306,33 @@
    ],
    "source": [
     "print(numbers)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 184,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 184,
+   },
    "outputs": [],
    "source": [
     "# extend\n",
     "others = list(\"fghjk\")\n",
     "alphabet.extend(others)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 185,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 185,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -328,32 +344,32 @@
    ],
    "source": [
     "print(alphabet)"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 186,
-   "outputs": [],
-   "source": [
-    "# remove\n",
-    "alphabet.remove(\"e\")"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
+   },
+   "outputs": [],
+   "source": [
+    "# remove\n",
+    "alphabet.remove(\"e\")"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 187,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -365,17 +381,17 @@
    ],
    "source": [
     "print(alphabet)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 188,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 188,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -389,17 +405,17 @@
     "# pop\n",
     "popped = numbers.pop(1)\n",
     "print(popped)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 189,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 189,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -411,60 +427,62 @@
    ],
    "source": [
     "print(numbers)"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "markdown",
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%% md\n"
+    }
+   },
    "source": [
     "# 元组"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%% md\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "markdown",
-   "source": [
-    "## 创建元组"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%% md\n"
     }
-   }
+   },
+   "source": [
+    "## 创建元组"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 190,
-   "outputs": [],
-   "source": [
-    "# literal\n",
-    "auth = (\"MY_ACCOUNT\", \"MY_PASSWORD\")"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
+   },
+   "outputs": [],
+   "source": [
+    "# literal\n",
+    "auth = (\"MY_ACCOUNT\", \"MY_PASSWORD\")"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 191,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "tuple"
+      "text/plain": [
+       "tuple"
+      ]
      },
      "execution_count": 191,
      "metadata": {},
@@ -473,17 +491,17 @@
    ],
    "source": [
     "type(auth)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 192,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 192,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -495,36 +513,38 @@
    ],
    "source": [
     "print(auth)"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 193,
-   "outputs": [],
-   "source": [
-    "# key word\n",
-    "database = tuple([\"DB_HOST\", \"DB_PORT\"])"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
+   },
+   "outputs": [],
+   "source": [
+    "# key word\n",
+    "database = tuple([\"DB_HOST\", \"DB_PORT\"])"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 194,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "tuple"
+      "text/plain": [
+       "tuple"
+      ]
      },
      "execution_count": 194,
      "metadata": {},
@@ -533,17 +553,17 @@
    ],
    "source": [
     "type(database)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 195,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 195,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -555,36 +575,38 @@
    ],
    "source": [
     "print(database)"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 196,
-   "outputs": [],
-   "source": [
-    "# avoid this !!\n",
-    "greet = \"Hello, 100gle\","
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
+   },
+   "outputs": [],
+   "source": [
+    "# avoid this !!\n",
+    "greet = \"Hello, 100gle\","
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 197,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "tuple"
+      "text/plain": [
+       "tuple"
+      ]
      },
      "execution_count": 197,
      "metadata": {},
@@ -593,17 +615,17 @@
    ],
    "source": [
     "type(greet)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 198,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 198,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -615,41 +637,41 @@
    ],
    "source": [
     "print(greet)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%% md\n"
+    }
+   },
+   "source": [
+    "# 字典"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%% md\n"
+    }
+   },
+   "source": [
+    "## 创建字典"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 199,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "markdown",
-   "source": [
-    "# 字典"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%% md\n"
-    }
-   }
-  },
-  {
-   "cell_type": "markdown",
-   "source": [
-    "## 创建字典"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%% md\n"
-    }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 199,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -674,17 +696,17 @@
     "from pprint import pprint\n",
     "\n",
     "pprint(info, indent=2)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 200,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 200,
+   },
    "outputs": [],
    "source": [
     "# keyword\n",
@@ -694,33 +716,35 @@
     "    greet=\"Hello, sspai!\",\n",
     "    account_stats=[1000, 10000, 100000],\n",
     ")"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "markdown",
-   "source": [
-    "## 索引与键值迭代"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%% md\n"
     }
-   }
+   },
+   "source": [
+    "## 索引与键值迭代"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 201,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "'100gle'"
+      "text/plain": [
+       "'100gle'"
+      ]
      },
      "execution_count": 201,
      "metadata": {},
@@ -729,21 +753,23 @@
    ],
    "source": [
     "info[\"name\"]"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 202,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 202,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "[1000, 10000, 100000]"
+      "text/plain": [
+       "[1000, 10000, 100000]"
+      ]
      },
      "execution_count": 202,
      "metadata": {},
@@ -752,17 +778,17 @@
    ],
    "source": [
     "info.get(\"account_stats\")  # [1000, 10000, 100000]"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 203,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 203,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -775,21 +801,23 @@
    "source": [
     "ret = info.get(\"address\")  # None\n",
     "print(ret)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 204,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 204,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "'Not Found'"
+      "text/plain": [
+       "'Not Found'"
+      ]
      },
      "execution_count": 204,
      "metadata": {},
@@ -798,17 +826,17 @@
    ],
    "source": [
     "info.get(\"address\", \"Not Found\")  # return \"Not Found\""
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 205,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 205,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -821,17 +849,17 @@
    "source": [
     "keys = info.keys()\n",
     "print(keys)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 206,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 206,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -844,17 +872,17 @@
    "source": [
     "values = info.values()\n",
     "print(values)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 207,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 207,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -873,45 +901,47 @@
     "print(items)\n",
     "for k, v in items:\n",
     "    print(f\"{k}: {v}\")"
-   ],
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%% md\n"
+    }
+   },
+   "source": [
+    "# 集合"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%% md\n"
+    }
+   },
+   "source": [
+    "## 创建集合"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 208,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "markdown",
-   "source": [
-    "# 集合"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%% md\n"
-    }
-   }
-  },
-  {
-   "cell_type": "markdown",
-   "source": [
-    "## 创建集合"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%% md\n"
-    }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 208,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "dict"
+      "text/plain": [
+       "dict"
+      ]
      },
      "execution_count": 208,
      "metadata": {},
@@ -922,21 +952,23 @@
     "# dict default literal\n",
     "d = {}\n",
     "type(d)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 209,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 209,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "dict"
+      "text/plain": [
+       "dict"
+      ]
      },
      "execution_count": 209,
      "metadata": {},
@@ -947,21 +979,23 @@
     "# dict literal\n",
     "d2 = {1: 2, 3: 4}\n",
     "type(d2)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 210,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 210,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "set"
+      "text/plain": [
+       "set"
+      ]
      },
      "execution_count": 210,
      "metadata": {},
@@ -972,17 +1006,17 @@
     "# set literal\n",
     "s = {1, 2}\n",
     "type(s)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 211,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 211,
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -997,49 +1031,51 @@
     "s = set()\n",
     "type(s)\n",
     "print(s)"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "markdown",
-   "source": [
-    "## 交集、并集和差集"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%% md\n"
     }
-   }
+   },
+   "source": [
+    "## 交集、并集和差集"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 212,
-   "outputs": [],
-   "source": [
-    "numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}\n",
-    "odds = {1, 3, 5, 7, 9}\n",
-    "evens = {2, 4, 6, 8, 10}"
-   ],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
+   },
+   "outputs": [],
+   "source": [
+    "numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}\n",
+    "odds = {1, 3, 5, 7, 9}\n",
+    "evens = {2, 4, 6, 8, 10}"
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 213,
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "True"
+      "text/plain": [
+       "True"
+      ]
      },
      "execution_count": 213,
      "metadata": {},
@@ -1049,21 +1085,23 @@
    "source": [
     "# union\n",
     "odds.union(evens) == numbers"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 214,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 214,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "{1, 3, 5, 7, 9}"
+      "text/plain": [
+       "{1, 3, 5, 7, 9}"
+      ]
      },
      "execution_count": 214,
      "metadata": {},
@@ -1073,21 +1111,23 @@
    "source": [
     "# intersection\n",
     "numbers.intersection(odds)"
-   ],
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 215,
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 215,
+   },
    "outputs": [
     {
      "data": {
-      "text/plain": "{2, 4, 6, 8, 10}"
+      "text/plain": [
+       "{2, 4, 6, 8, 10}"
+      ]
      },
      "execution_count": 215,
      "metadata": {},
@@ -1097,25 +1137,19 @@
    "source": [
     "# difference\n",
     "numbers.difference(odds)"
-   ],
-   "metadata": {
-    "collapsed": false,
-    "pycharm": {
-     "name": "#%%\n"
-    }
-   }
+   ]
   },
   {
    "cell_type": "code",
    "execution_count": 215,
-   "outputs": [],
-   "source": [],
    "metadata": {
     "collapsed": false,
     "pycharm": {
      "name": "#%%\n"
     }
-   }
+   },
+   "outputs": [],
+   "source": []
   }
  ],
  "metadata": {
@@ -1139,4 +1173,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 0
-}
\ No newline at end of file
+}