# How to make an observation numbering in bold?

I'm writing a paper in LIPIcs template.

\newtheorem{observation}[theorem]{\textbf{Observation}}

\newcommand{\robs}[1]{Observation~\ref{#1}}
\newcommand{\rfig}[1]{Fig.~\ref{#1}}
\newcommand{\rlem}[1]{Lemma~\ref{#1}}
\newcommand{\rdef}[1]{Definition~\ref{#1}}
\newcommand{\rthm}[1]{Theorem~\ref{#1}}
\newcommand{\rpro}[1]{Proposition~\ref{#1}}
\newcommand{\rcor}[1]{Corollary~\ref{#1}}
\newcommand{\rse}[1]{Section~\ref{#1}}

However the observation number is not in bold. I want to make the observation number bold.

How can I do this?

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 some of the answers so far assume that you want the heading of the observation report to be bold, but your description sounds more like you want the cross reference number bold irrespective of the style of the heading. please clarify. – barbara beeton Sep 25 '12 at 18:51

You can use the definition style (available though amsthm internally loaded by the class) for your observation theorem-like structure:

\documentclass[a4paper,UKenglish]{lipics}

\theoremstyle{definition}
\newtheorem{observation}[theorem]{Observation}

\begin{document}

\begin{observation}
test
\end{observation}

\end{document}

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A small change in your definition will do the job:

\newcommand{\robs}[1]{Observation~\textbf{\ref{#1}}}
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lipics uses amsthm to set its theorems. You can redefine the generic theorem number setting macro \@upn, which defaults to \textup:

\documentclass[english]{lipics}
\newtheorem{observation}[theorem]{\textbf{Observation}}
\makeatletter
\let\@upn\textbf% \textup -> \textbf
\makeatother
\begin{document}
\begin{observation}
This is an observation.
\end{observation}
\end{document}

A more intuitive way is to redefine the "theorem head spec" (argument #9 in \newtheoremstyle), use an existing style (like in Gonzalo's answer) or define a new theorem style altogether.

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