clarify lhs for (read)

book.tex

@@ -1633,10 +1633,11 @@ functionality in this file as the \emph{runtime system}, or simply
 \emph{runtime} for short. When compiling your generated x86-64
 assembly code, you will need to compile \code{runtime.c} and link it
 in. For our purposes of code generation, all you need to do is
-translate an assignment of \key{read} to some left-hand side
-$\itm{lhs}$ into call to the \code{read\_int} function followed by a
-move from \code{rax} into $\itm{lhs}$. (Recall that the return value
-of a function is typically placed in the \code{rax} register.)  \\
+translate an assignment of \key{read} to some variable $\itm{lhs}$
+(for left-hand side) into call to the \code{read\_int} function
+followed by a move from \code{rax} into the left-hand side. Also,
+recall that the return value of a function is typically placed in the
+\code{rax} register.  \\
 \begin{tabular}{lll}
 \begin{minipage}{0.4\textwidth}
 \begin{lstlisting}
@@ -1649,7 +1650,7 @@ $\Rightarrow$
 \begin{minipage}{0.4\textwidth}
 \begin{lstlisting}
 (callq read_int)
-(movq (reg rax) |$\itm{lhs}$|)
+(movq (reg rax) (var |$\itm{lhs}$|))
 \end{lstlisting}
 \end{minipage}
 \end{tabular} \\
@@ -1966,7 +1967,7 @@ $L_{\mathtt{after}}$ set to make the figure easy to read.
 |$\{ w, x, y \}$|
 |$\{ w, y, z \}$|
 |$\{ y, z \}$|
-|$\{ y \}$|
+|$\{ y, \key{rax} \}$|
 |$\{\}$|
 \end{lstlisting}
 \end{minipage}