Minor fixes

book/book.tex

@@ -32,7 +32,7 @@
 \title{Think Python}
 \author{Allen B. Downey}
 \newcommand{\thetitle}{Think Python: How to Think Like a Computer Scientist}
-\newcommand{\theversion}{2nd Edition, Version 2.2.21}
+\newcommand{\theversion}{2nd Edition, Version 2.2.23}
 \newcommand{\thedate}{}
 
 % these styles get translated in CSS for the HTML version
@@ -8537,8 +8537,8 @@ \section{Exercises}
 find the word or conclude that it's not there.
 
 Write a function called \verb"in_bisect" that takes a sorted list
-and a target value and returns the index of the value
-in the list if it's there, or {\tt None} if it's not.
+and a target value and returns {\tt True} if the word is
+in the list and {\tt False} if it's not.
 \index{bisect module}
 \index{module!bisect}
 
@@ -15133,7 +15133,7 @@ \section{Generator expressions}
 %
 The generator object keeps track of where it is in the sequence,
 so the {\tt for} loop picks up where {\tt next} left off.  Once the
-generator is exhausted, it continues to raise {\tt StopException}:
+generator is exhausted, it continues to raise {\tt StopIteration}:
 
 \begin{verbatim}
 >>> next(g)