Don't use function name subscripts formatted as variable names

chapters/dae.tex

@@ -25,14 +25,14 @@ \chapter{Modelica DAE Representation}\doublelabel{modelica-dae-representation}
 obtained consisting of differential, algebraic and discrete equations of
 the following form where ($v := \lbrack \dot{x}; x; y; t; m; \text{\lstinline!pre!}(m); p\rbrack$):
 \begin{subequations}
-\begin{equation}
-c:=f_{\mathrm{c}}(\mathit{relation}(v))\label{eq:crossing}
+\begin{equation}\label{eq:crossing}
+c := f_{\mathrm{c}}(\mathit{relation}(v))
 \end{equation}
 \begin{equation}
 m := f_{\mathrm{m}}(v, c)
 \end{equation}
-\begin{equation}
-0=f_x(v, c)\label{eq:dae}
+\begin{equation}\label{eq:dae}
+0 = f_{\mathrm{x}}(v, c)
 \end{equation}
 \label{eq:hydrid-dae}
 \end{subequations}