Say 'clock variables' instead of 'Clock-variables'

chapters/synchronous.tex

@@ -475,7 +475,7 @@ \section{Clock Constructors}\label{clock-constructors}
 
 Clock variables can be used in a restricted form of expressions.
 Generally, every expression switching between clock variables must have parameter variability (in order that clock analysis can be performed when translating a model).
-Thus subscripts on Clock-variables and conditions of if-then-else switching between Clock-variables must be parameter expressions, and there are similar restrictions for sub-clock conversion operators \cref{sub-clock-conversion-operators}.
+Thus subscripts on clock variables and conditions of if-then-else switching between clock variables must be parameter expressions, and there are similar restrictions for sub-clock conversion operators \cref{sub-clock-conversion-operators}.
 Otherwise, the following expressions are allowed:
 \begin{itemize}
 \item