Updating the notebooks

Author: AllenDowney

chapters/chap12.ipynb

@@ -1827,7 +1827,7 @@
  "metadata": {},
  "source": [
  "Dictionaries provide a method called `setdefault` that we can use to do the same thing more concisely.\n",
- "Ask a virtual assistant how it works, or copy `add_word` into a virtual assistant and ask \"Can you rewrite this using `setdefault`?\"\n",
+ "Ask a virtual assistant how it works, or copy `add_bigram` into a virtual assistant and ask \"Can you rewrite this using `setdefault`?\"\n",
  "\n",
  "In this chapter we implemented Markov chain text analysis and generation.\n",
  "If you are curious, you can ask a virtual assistant for more information on the topic.\n",