Use \firstuse when defining clock partitioning terminology

chapters/synchronous.tex

@@ -826,19 +826,11 @@ \section{Clock Partitioning}\label{clock-partitioning}
 
 Every clocked variable is uniquely associated with exactly one clock.
 
-After model flattening, every equation in an equation section, every
-expression and every algorithm section is either continuous-time, or it
-is uniquely associated with exactly one clock. In the latter case it is
-called a clocked equation, a clocked expression or clocked algorithm
-section respectively. The associated clock is either explicitly defined
-by a when-clause, see \cref{sub-clock-conversion-operators}, or it is implicitly defined by the
-requirement that a clocked equation, a clocked expression and a clocked
-algorithm section must have the same clock as the variables used in them
-with exception of the expressions used as first arguments in the
-conversion operators of \cref{partitioning-operators}. Clock inference means to infer the
-clock of a variable, an equation, an expression or an algorithm section
-if the clock is not explicitly defined and is deduced from the required
-properties in the previous two paragraphs.
+After model flattening, every equation in an equation section, every expression and every algorithm section is either continuous-time, or it is uniquely associated with exactly one clock.
+% Warning: The uses of \firstuse below aren't the first time these terms are used.
+In the latter case it is called a \firstuse{clocked equation}, a \firstuse{clocked expression} or \firstuse{clocked algorithm} section respectively.
+The associated clock is either explicitly defined by a when-clause, see \cref{sub-clock-conversion-operators}, or it is implicitly defined by the requirement that a clocked equation, a clocked expression and a clocked algorithm section must have the same clock as the variables used in them with exception of the expressions used as first arguments in the conversion operators of \cref{partitioning-operators}.
+\firstuse{Clock inference} means to infer the clock of a variable, an equation, an expression or an algorithm section if the clock is not explicitly defined and is deduced from the required properties in the previous two paragraphs.
 
 All variables in an expression without clock conversion operators must
 have the same clock to infer the clocks for each variable and