Add space between commas in listing

chapters/statements.tex

@@ -143,7 +143,7 @@ \subsubsection{Assignments from Called Functions with Multiple Results}\label{as
 
 It is possible to omit receiving variables from this list:
 \begin{lstlisting}[language=modelica]
-(out1,, out3) := function_name(in1, in2, in3, in4);
+(out1, , out3) := function_name(in1, in2, in3, in4);
 \end{lstlisting}
 
 \begin{example}