Update chapters/classes.tex

Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>

chapters/classes.tex

@@ -1400,7 +1400,7 @@ \section{Predefined Types and Classes}\label{predefined-types-and-classes}
 \begin{definition}[Fallback value]\label{def:fallback-value}\index{fallback value}
 When the start-value is needed and the \lstinline!start!-attribute is not provided, the fall-back value is used instead.
 The fall-back value can be be used as guess-value in system of equations and when initializing variables in algorithm sections.
-The fall-back value for variables of the different predefined types are defined below.
+The fallback values for variables of the different predefined types are defined below.
 \end{definition}
 
 \subsection{Real Type}\label{real-type}