Remove reference to TurtleWorld

AllenDowney · web-flow · commit 0c36e079ed0e · 2020-01-10T12:30:00.000-05:00
diff --git a/book/book.tex b/book/book.tex
@@ -2990,7 +2990,7 @@ \section{Simple repetition}
 
 \section{Exercises}
 
-The following is a series of exercises using TurtleWorld.  They
+The following is a series of exercises using the {\tt turtle} module.  They
 are meant to be fun, but they have a point, too.  While you are
 working on them, think about what the point is.
 
@@ -4375,7 +4375,7 @@ \section{Exercises}
 
 The following exercises use the {\tt turtle} module, described in
 Chapter~\ref{turtlechap}:
-\index{TurtleWorld}
+\index{turtle module}
 
 \begin{exercise}
 
