diff --git a/chapters/operatorsandexpressions.tex b/chapters/operatorsandexpressions.tex
index 5c0d03677..d49f02581 100644
--- a/chapters/operatorsandexpressions.tex
+++ b/chapters/operatorsandexpressions.tex
@@ -1158,10 +1158,12 @@ \subsection{Event-Related Operators with Function Syntax}\doublelabel{event-rela
 positive number.\\ \hline
 
 % pre
-\lstinline!pre(y)! & Returns the \emph{left limit} $y(t\textsuperscript{pre})$ of
+\lstinline!pre(y)! & Returns the \emph{left limit} $y(t^{-})$ of
 variable $y(t)$ at a time instant $t$. At an event instant,
-$y(t\textsuperscript{pre})$ is the value of y after the last event
-iteration at time instant $t$ (see comment below). The \lstinline!pre()! operator can
+$y(t^{-})$ is the value of y after the last event
+iteration at time instant $t$ (see comment below). 
+Any subscripts in the component expression $y$ must be parameter expressions.
+The \lstinline!pre()! operator can
 be applied if the following three conditions are fulfilled
 simultaneously: (a) variable $y$ is either a subtype of a simple type or
 is a record component, (b) $y$ is a discrete-time expression (c) the