typo: update "later" -> "latter"

book.tex

@@ -2975,7 +2975,7 @@ become local variables whose scope is the entire program, which would
 confuse variables with the same name.}
 %
 \racket{We place \key{remove\_complex\_operands} before \key{explicate\_control}
-because the later removes the \key{let} form, but it is convenient to
+because the latter removes the \key{let} form, but it is convenient to
 use \key{let} in the output of \key{remove\_complex\_operands}.}
 %
 \racket{The ordering of \key{uniquify} with respect to