Clarify definition of 'clocked state variable'

chapters/synchronous.tex

@@ -553,8 +553,7 @@ \section{Clock Constructors}\label{clock-constructors}
 
 \section{Clocked State Variables}\label{clocked-state-variable}
 
-The previous value of a clocked variable can be accessed with the
-previous operator. Such a variable is called a clocked state variable.
+The previous value of a clocked variable can be accessed with the \lstinline!previous! operator.  A variable to which \lstinline!previous! has been applied is called a \firstuse{clocked state variable}.
 
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