Update book.tex

AllenDowney · web-flow · commit 323244123efb · 2016-06-30T09:27:56.000-04:00
Correction from Tim Voets
diff --git a/book/book.tex b/book/book.tex
@@ -4050,7 +4050,7 @@ \section{Infinite recursion}
 previous chapter.  When the error occurs, there are 1000
 {\tt recurse} frames on the stack!
 
-If you write encounter an infinite recursion by accident, review
+If you encounter an infinite recursion by accident, review
 your function to confirm that there is a base case that does not
 make a recursive call.  And if there is a base case, check whether
 you are guaranteed to reach it.
