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I'm trying to get:

First_Section
Second_Section
1 Red Subsection
2 Blue Subsection

rather than:

First_Section
Second_Section
0.1 Red Subsection
0.2 Blue Subsection

I've tried:

\section*{First_Section}
\section*{Second_Section}
\subsection{Red Subsection}
\subsection{Blue Subsection}

but this ...