put substraction into Cif

book.tex

@@ -7084,7 +7084,7 @@ an assignment statement followed by a $\Tail$ expression, a
 \begin{array}{lcl}
 \Atm &::=& \gray{ \Int \MID \Var } \MID \itm{bool} \\
 \itm{cmp} &::= & \code{eq?} \MID \code{<} \MID \code{<=} \MID \code{>} \MID \code{>=} \\
-\Exp &::=& \gray{ \Atm \MID \key{(read)} \MID \key{(-}~\Atm\key{)} \MID \key{(+}~\Atm~\Atm\key{)} } \\
+\Exp &::=& \gray{ \Atm \MID \key{(read)} \MID \key{(-}~\Atm\key{)} \MID \key{(+}~\Atm~\Atm\key{)} \MID \key{(-}~\Atm~\Atm\key{)} } \\
    &\MID& \LP \key{not}~\Atm \RP \MID \LP \itm{cmp}~\Atm~\Atm\RP \\
 \Stmt &::=& \gray{ \Var~\key{=}~\Exp\key{;} } \\
 \Tail &::= & \gray{ \key{return}~\Exp\key{;} \MID \Stmt~\Tail }