Add suggested 'The' at start of sentence

Co-authored-by: Hans Olsson <HansOlsson@users.noreply.github.com>

chapters/equations.tex

@@ -167,7 +167,7 @@ \subsection{Connect-Equations}\label{connect-equations}
 
 \subsection{If-Equations}\label{if-equations}
 
-\lstinline!if!-equations\index{if@\robustinline{if}!equation}\index{then@\robustinline{then}!if-equation@\robustinline{if}-equation}\index{else@\robustinline{else}!if-equation@\robustinline{if}-equation}\index{elseif@\robustinline{elseif}!if-equation@\robustinline{if}-equation} have the following syntax:
+The \lstinline!if!-equations\index{if@\robustinline{if}!equation}\index{then@\robustinline{then}!if-equation@\robustinline{if}-equation}\index{else@\robustinline{else}!if-equation@\robustinline{if}-equation}\index{elseif@\robustinline{elseif}!if-equation@\robustinline{if}-equation} have the following syntax:
 \begin{lstlisting}[language=grammar]
 if expression then
    { equation ";" }