diff --git a/ThinkPythonNotebooks.zip b/ThinkPythonNotebooks.zip
index 4be25fa..f5c7866 100644
Binary files a/ThinkPythonNotebooks.zip and b/ThinkPythonNotebooks.zip differ
diff --git a/chapters/chap00.ipynb b/chapters/chap00.ipynb
index b42d9c0..e7c283c 100644
--- a/chapters/chap00.ipynb
+++ b/chapters/chap00.ipynb
@@ -50,7 +50,7 @@
     "\n",
     "Writing this book, I tried to be careful with the vocabulary.\n",
     "I define each term when it first appears.\n",
-    "And there is a glossary that the end of each chapter that reviews the terms that were introduced.\n",
+    "And there is a glossary at the end of each chapter that reviews the terms that were introduced.\n",
     "\n",
     "I also tried to be concise.\n",
     "The less mental effort it takes to read the book, the more capacity you will have for programming.\n",
diff --git a/chapters/chap10.ipynb b/chapters/chap10.ipynb
index e1de3af..742da86 100644
--- a/chapters/chap10.ipynb
+++ b/chapters/chap10.ipynb
@@ -1364,7 +1364,7 @@
    "id": "170f1deb",
    "metadata": {},
    "source": [
-    "### Ask an assistant\n",
+    "### Ask a virtual assistant\n",
     "\n",
     "In this chapter, I said the keys in a dictionary have to be hashable and I gave a short explanation. If you would like more details, ask a virtual assistant, \"Why do keys in Python dictionaries have to be hashable?\"\n",
     "\n",
diff --git a/chapters/chap12.ipynb b/chapters/chap12.ipynb
index 49c55ce..f2d5d23 100644
--- a/chapters/chap12.ipynb
+++ b/chapters/chap12.ipynb
@@ -80,7 +80,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": 2,
    "id": "4cd1c980",
    "metadata": {
     "tags": []
@@ -103,7 +103,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": 3,
    "id": "52ebfe94",
    "metadata": {
     "tags": []
@@ -116,7 +116,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 4,
    "id": "49cfc352",
    "metadata": {
     "tags": []
@@ -142,7 +142,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": 5,
    "id": "44e53ce6",
    "metadata": {},
    "outputs": [],
@@ -152,7 +152,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": 6,
    "id": "50d1fafa",
    "metadata": {
     "tags": []
@@ -173,7 +173,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 9,
+   "execution_count": 7,
    "id": "16d24028",
    "metadata": {},
    "outputs": [],
@@ -201,7 +201,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 88,
+   "execution_count": 8,
    "id": "1668e6bd",
    "metadata": {},
    "outputs": [],
@@ -241,7 +241,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": 9,
    "id": "ed5f0a43",
    "metadata": {},
    "outputs": [],
@@ -261,7 +261,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 12,
+   "execution_count": 10,
    "id": "a9df2aeb",
    "metadata": {},
    "outputs": [],
@@ -283,7 +283,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 13,
+   "execution_count": 11,
    "id": "b138b123",
    "metadata": {},
    "outputs": [],
@@ -305,7 +305,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 14,
+   "execution_count": 12,
    "id": "fe65df44",
    "metadata": {},
    "outputs": [],
@@ -324,7 +324,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 15,
+   "execution_count": 13,
    "id": "b47a87cf",
    "metadata": {},
    "outputs": [],
@@ -347,7 +347,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 16,
+   "execution_count": 14,
    "id": "348949be",
    "metadata": {},
    "outputs": [],
@@ -366,7 +366,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 15,
    "id": "06121901",
    "metadata": {},
    "outputs": [],
@@ -385,7 +385,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 18,
+   "execution_count": 16,
    "id": "881ed9f8",
    "metadata": {},
    "outputs": [],
@@ -403,7 +403,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 19,
+   "execution_count": 17,
    "id": "ab5d2fed",
    "metadata": {},
    "outputs": [],
@@ -421,7 +421,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 20,
+   "execution_count": 18,
    "id": "2fdfb936",
    "metadata": {},
    "outputs": [],
@@ -446,7 +446,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 21,
+   "execution_count": 19,
    "id": "3104d191",
    "metadata": {},
    "outputs": [],
@@ -474,7 +474,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 22,
+   "execution_count": 20,
    "id": "4fba7d1c",
    "metadata": {},
    "outputs": [],
@@ -502,7 +502,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 23,
+   "execution_count": 21,
    "id": "4be34c95",
    "metadata": {},
    "outputs": [],
@@ -525,7 +525,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 24,
+   "execution_count": 22,
    "id": "8efe7c4c",
    "metadata": {},
    "outputs": [],
@@ -543,7 +543,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 25,
+   "execution_count": 23,
    "id": "79c17341",
    "metadata": {},
    "outputs": [],
@@ -574,7 +574,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 26,
+   "execution_count": 24,
    "id": "838bcb4f",
    "metadata": {},
    "outputs": [],
@@ -593,7 +593,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 27,
+   "execution_count": 25,
    "id": "90c45e7e",
    "metadata": {},
    "outputs": [],
@@ -617,7 +617,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 28,
+   "execution_count": 26,
    "id": "e106be95",
    "metadata": {},
    "outputs": [],
@@ -635,7 +635,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 29,
+   "execution_count": 27,
    "id": "8101a510",
    "metadata": {},
    "outputs": [],
@@ -655,7 +655,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 30,
+   "execution_count": 28,
    "id": "c046117b",
    "metadata": {
     "tags": []
@@ -697,7 +697,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 31,
+   "execution_count": 29,
    "id": "edd8ff1c",
    "metadata": {
     "tags": []
@@ -717,7 +717,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 32,
+   "execution_count": 30,
    "id": "67ef3e08",
    "metadata": {},
    "outputs": [],
@@ -735,7 +735,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 33,
+   "execution_count": 31,
    "id": "471d58e9",
    "metadata": {},
    "outputs": [],
@@ -755,7 +755,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 34,
+   "execution_count": 32,
    "id": "4d4c3538",
    "metadata": {},
    "outputs": [],
@@ -778,7 +778,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 35,
+   "execution_count": 33,
    "id": "8b42e014",
    "metadata": {},
    "outputs": [],
@@ -796,7 +796,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 36,
+   "execution_count": 34,
    "id": "f48be152",
    "metadata": {},
    "outputs": [],
@@ -817,7 +817,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 37,
+   "execution_count": 35,
    "id": "5716f967",
    "metadata": {},
    "outputs": [],
@@ -838,7 +838,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 38,
+   "execution_count": 36,
    "id": "b37219f5",
    "metadata": {},
    "outputs": [],
@@ -880,7 +880,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 39,
+   "execution_count": 37,
    "id": "75b548a9",
    "metadata": {},
    "outputs": [],
@@ -890,7 +890,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 40,
+   "execution_count": 38,
    "id": "2bfa31ae",
    "metadata": {
     "tags": []
@@ -913,7 +913,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 41,
+   "execution_count": 39,
    "id": "6f5d5c1c",
    "metadata": {},
    "outputs": [],
@@ -932,7 +932,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 42,
+   "execution_count": 40,
    "id": "1445068b",
    "metadata": {},
    "outputs": [],
@@ -952,7 +952,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 43,
+   "execution_count": 41,
    "id": "4fc47ecd",
    "metadata": {
     "tags": []
@@ -974,7 +974,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 44,
+   "execution_count": 42,
    "id": "91ae9d4c",
    "metadata": {},
    "outputs": [],
@@ -993,7 +993,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 45,
+   "execution_count": 43,
    "id": "8bf595c1",
    "metadata": {},
    "outputs": [],
@@ -1016,7 +1016,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 46,
+   "execution_count": 44,
    "id": "22953b65",
    "metadata": {},
    "outputs": [],
@@ -1034,7 +1034,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 47,
+   "execution_count": 45,
    "id": "1c7cdf4d",
    "metadata": {},
    "outputs": [],
@@ -1052,7 +1052,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 48,
+   "execution_count": 46,
    "id": "a7a3aa42",
    "metadata": {},
    "outputs": [],
@@ -1071,7 +1071,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 49,
+   "execution_count": 47,
    "id": "c4286fb3",
    "metadata": {},
    "outputs": [],
@@ -1111,7 +1111,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 50,
+   "execution_count": 48,
    "id": "d8ee02f6",
    "metadata": {},
    "outputs": [],
@@ -1131,7 +1131,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 51,
+   "execution_count": 49,
    "id": "bfdb1de1",
    "metadata": {},
    "outputs": [],
@@ -1158,7 +1158,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 52,
+   "execution_count": 50,
    "id": "2e73df79",
    "metadata": {},
    "outputs": [],
@@ -1176,7 +1176,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 53,
+   "execution_count": 51,
    "id": "495ad429",
    "metadata": {},
    "outputs": [],
@@ -1206,7 +1206,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 54,
+   "execution_count": 52,
    "id": "c1224061",
    "metadata": {},
    "outputs": [],
@@ -1228,7 +1228,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 55,
+   "execution_count": 53,
    "id": "4296485a",
    "metadata": {},
    "outputs": [],
@@ -1247,7 +1247,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 56,
+   "execution_count": 54,
    "id": "e03fd803",
    "metadata": {
     "tags": []
@@ -1259,7 +1259,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 57,
+   "execution_count": 55,
    "id": "f6ee1840",
    "metadata": {},
    "outputs": [],
@@ -1282,7 +1282,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 58,
+   "execution_count": 56,
    "id": "d6c65d79",
    "metadata": {},
    "outputs": [],
@@ -1312,7 +1312,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 59,
+   "execution_count": 57,
    "id": "3171d592",
    "metadata": {},
    "outputs": [],
@@ -1335,7 +1335,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 60,
+   "execution_count": 58,
    "id": "3321e6a4",
    "metadata": {},
    "outputs": [],
@@ -1353,7 +1353,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 61,
+   "execution_count": 59,
    "id": "e4e55c71",
    "metadata": {},
    "outputs": [],
@@ -1372,7 +1372,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 62,
+   "execution_count": 60,
    "id": "f25dcb5e",
    "metadata": {},
    "outputs": [],
@@ -1391,7 +1391,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 63,
+   "execution_count": 61,
    "id": "990354a0",
    "metadata": {},
    "outputs": [],
@@ -1413,7 +1413,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 64,
+   "execution_count": 62,
    "id": "b9371452",
    "metadata": {},
    "outputs": [],
@@ -1441,7 +1441,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 65,
+   "execution_count": 63,
    "id": "8c3f45c2",
    "metadata": {},
    "outputs": [],
@@ -1464,7 +1464,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 66,
+   "execution_count": 64,
    "id": "641990a3",
    "metadata": {},
    "outputs": [],
@@ -1487,7 +1487,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 67,
+   "execution_count": 65,
    "id": "9322a49a",
    "metadata": {},
    "outputs": [],
@@ -1509,7 +1509,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 68,
+   "execution_count": 66,
    "id": "45a60c52",
    "metadata": {},
    "outputs": [],
@@ -1533,7 +1533,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 69,
+   "execution_count": 67,
    "id": "3e86102c",
    "metadata": {
     "tags": []
@@ -1553,7 +1553,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 70,
+   "execution_count": 68,
    "id": "e49d52f7",
    "metadata": {},
    "outputs": [],
@@ -1590,7 +1590,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 71,
+   "execution_count": 69,
    "id": "15108884",
    "metadata": {},
    "outputs": [],
@@ -1602,7 +1602,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 72,
+   "execution_count": 70,
    "id": "747a41be",
    "metadata": {
     "tags": []
@@ -1626,7 +1626,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 73,
+   "execution_count": 71,
    "id": "5a4682dc",
    "metadata": {},
    "outputs": [],
@@ -1647,7 +1647,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 74,
+   "execution_count": 72,
    "id": "36ee0f76",
    "metadata": {},
    "outputs": [],
@@ -1782,7 +1782,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 73,
    "id": "05752b6d",
    "metadata": {
     "tags": []
@@ -1807,7 +1807,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 75,
+   "execution_count": 74,
    "id": "a4365ac0",
    "metadata": {},
    "outputs": [],
@@ -1850,7 +1850,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 76,
+   "execution_count": 75,
    "id": "f38a61ff",
    "metadata": {},
    "outputs": [],
@@ -1860,7 +1860,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 77,
+   "execution_count": 76,
    "id": "d047e546",
    "metadata": {},
    "outputs": [],
@@ -1880,7 +1880,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 78,
+   "execution_count": 77,
    "id": "6b8932ee",
    "metadata": {
     "tags": []
@@ -1908,7 +1908,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 79,
+   "execution_count": 78,
    "id": "44c3f0d8",
    "metadata": {
     "tags": []
@@ -1932,7 +1932,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 80,
+   "execution_count": 79,
    "id": "3fcf85f4",
    "metadata": {},
    "outputs": [],
@@ -1950,7 +1950,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 81,
+   "execution_count": 80,
    "id": "d9e554e3",
    "metadata": {},
    "outputs": [],
@@ -1975,7 +1975,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 82,
+   "execution_count": 81,
    "id": "8c2ee21c",
    "metadata": {
     "tags": []
@@ -2003,7 +2003,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 83,
+   "execution_count": 82,
    "id": "b13384e3",
    "metadata": {
     "tags": []
@@ -2023,7 +2023,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 84,
+   "execution_count": 83,
    "id": "62c2177f",
    "metadata": {},
    "outputs": [],
@@ -2057,7 +2057,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 85,
+   "execution_count": 84,
    "id": "64e11f26",
    "metadata": {
     "tags": []
@@ -2081,7 +2081,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 86,
+   "execution_count": 85,
    "id": "fe2d93fa",
    "metadata": {},
    "outputs": [],
@@ -2109,7 +2109,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 89,
+   "execution_count": 86,
    "id": "22210a5c",
    "metadata": {},
    "outputs": [],
diff --git a/chapters/chap15.ipynb b/chapters/chap15.ipynb
index 52fb9c8..f7dfa60 100644
--- a/chapters/chap15.ipynb
+++ b/chapters/chap15.ipynb
@@ -373,7 +373,7 @@
    "id": "e6a18c76",
    "metadata": {},
    "source": [
-    "Now that we have `Time.from_seconds`, we can use it to write `add_time` as a method.\n",
+    "Now that we have `Time.int_to_time`, we can use it to write `add_time` as a method.\n",
     "Here's the function from the previous chapter."
    ]
   },
@@ -409,7 +409,7 @@
     "\n",
     "    def add_time(self, hours, minutes, seconds):\n",
     "        duration = make_time(hours, minutes, seconds)\n",
-    "        seconds = time_to_int(self) + time_to_int(duration)\n",
+    "        seconds = Time.time_to_int(self) + Time.time_to_int(duration)\n",
     "        return Time.int_to_time(seconds)"
    ]
   },
@@ -431,7 +431,7 @@
    "outputs": [],
    "source": [
     "end = start.add_time(1, 32, 0)\n",
-    "print_time(end)"
+    "end.print_time()"
    ]
   },
   {
@@ -836,7 +836,7 @@
     "\n",
     "    def is_after(self, other):\n",
     "        assert self.is_valid(), 'self is not a valid Time'\n",
-    "        assert other.is_valid(), 'self is not a valid Time'\n",
+    "        assert other.is_valid(), 'other is not a valid Time'\n",
     "        return self.time_to_int() > other.time_to_int()"
    ]
   },
@@ -924,7 +924,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 36,
    "id": "3115ea33",
    "metadata": {
     "tags": []
@@ -960,7 +960,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 36,
+   "execution_count": 37,
    "id": "133d7679",
    "metadata": {},
    "outputs": [],
@@ -992,7 +992,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 37,
+   "execution_count": 38,
    "id": "3c9f3777-4869-481e-9f4e-4223d6028913",
    "metadata": {},
    "outputs": [],
@@ -1012,7 +1012,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 38,
+   "execution_count": 39,
    "id": "fd4b2521-aa71-45da-97eb-ce62ce2714ad",
    "metadata": {
     "tags": []
@@ -1025,7 +1025,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 39,
+   "execution_count": 40,
    "id": "ee3f1294-cad1-406b-a574-045ad2b84294",
    "metadata": {
     "tags": []
@@ -1038,7 +1038,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 40,
+   "execution_count": 41,
    "id": "ac093f7b-83cf-4488-8842-5c71bcfa35ec",
    "metadata": {
     "tags": []
@@ -1050,7 +1050,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 41,
+   "execution_count": 42,
    "id": "7e7cb5e1-631f-4b1e-874f-eb16d4792625",
    "metadata": {
     "tags": []
diff --git a/chapters/chap16.ipynb b/chapters/chap16.ipynb
index 57f3d41..eb84e1c 100644
--- a/chapters/chap16.ipynb
+++ b/chapters/chap16.ipynb
@@ -234,7 +234,7 @@
    "id": "a7a635ee",
    "metadata": {},
    "source": [
-    "In the same way that the built in function `sort` modifies a list, and the `sorted` function creates a new list, now we have a `translate` method that modifies a `Point` and a `translated` method that creates a new one.\n",
+    "In the same way that the `sort` method modifies a list and the `sorted` function creates a new list, now we have a `translate` method that modifies a `Point` and a `translated` method that creates a new one.\n",
     "\n",
     "Here's an example:"
    ]
diff --git a/chapters/chap18.ipynb b/chapters/chap18.ipynb
index 41d5fc1..3027822 100644
--- a/chapters/chap18.ipynb
+++ b/chapters/chap18.ipynb
@@ -1661,7 +1661,7 @@
    "id": "07be77f3",
    "metadata": {},
    "source": [
-    "In this example, the value of `kwargs` is printed, but otherwise is has no effect.\n",
+    "In this example, the value of `kwargs` is printed, but otherwise it has no effect.\n",
     "\n",
     "But the `**` operator can also be used in an argument list to unpack a dictionary.\n",
     "For example, here's a version of `mean` that packs any keyword arguments it gets and then unpacks them as keyword arguments for `sum`."