[Tex/LaTex] Theorem numbers in bold

boldnumberingtheorems

With the standard theorem-like environemnts (at least when using amsthm), one obtains something like

Theorem 2.3.

where "Theorem" is in bold but "2.3." is not. I would like to have the number in bold too. A first solution may look like

\newtheorem{thm}{Theorem}[section]
\renewcommand{\thethm}{\textbf{\arabic{section}.\arabic{thm}}}

The problem with this solution is that every reference to a theorem number will be in bold as well, and I don't want this inside the text.

Is there a way to have only the numbers in theorem headings in bold?

EDIT As it was pointed out, my actual example is slightly more complicated than that. I am using a modified theorem style; a minimal example follows

\documentclass[reqno]{amsart}

\usepackage{amsthm, lipsum}
\swapnumbers

\newtheoremstyle{dotless-thm}
{3pt}
{3pt}
{\it}
{}
{\bfseries}
{}
{.5em}
{}

\theoremstyle{dotless-thm}
\newtheorem{thm}{Theorem}[section]

\begin{document}
\begin{thm}
\lipsum
\end{thm}
\end{document}

Even though I use bfseries for the theorem body font, the number appears in normal font.

Best Answer

You can redefine the internal command \swappedhead of amsart.cls which changes the number font when the \swapnumbers command is invoked. This can be done adding the lines between \makeatletter and \makeatother in my example code:

\documentclass{amsart}
\usepackage{amsthm}
\swapnumbers

\makeatletter
\def\swappedhead#1#2#3{%
  % original definition:
  % \thmnumber{\@upn{\the\thm@headfont#2\@ifnotempty{#1}{.~}}}%
  % change:
  \thmnumber{\@upn{\the\thm@headfont#2\@ifnotempty{#1}{.~}}}%
  \thmname{#1}%
  \thmnote{ {\the\thm@notefont(#3)}}}
\makeatother

\newtheoremstyle{dotless-thm}
  {3pt}
  {3pt}
  {\itshape}
  {}
  {\bfseries}
  {}
  {.5em}
  {}
\theoremstyle{dotless-thm}
\newtheorem{theo}{Theorem}

\begin{document}

\begin{theo}
Test
\end{theo}
\end{document}

EDIT: as Seamus has suggested in his answer, the fact that the number font for theorem-like structures changes if the \swapnumbers switch is in use is a feature provided by the AMS document classes.

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