# Bold math using bm within breqn results in compilation error

Combining bm with breqn produces following error

! TeX capacity exceeded, sorry [input stack size=5000].
\bm@command ->
\mathchar 30049 \bin@break \mathchar 9259 \mathchar 30050 \let...
l.8 \bm{a + b = c}
!  ==> Fatal error occurred, no output PDF file produced!


It happens only if I enclose equal sign in \bm, like in this example

\begin{dmath*}[compact]
\bm{a + b = c}
\end{dmath*}


Everything works smoothly if I skip equal sign, like here

\begin{dmath*}[compact]
\bm{a + b} = \bm{c}
\end{dmath*}


However compilation of \bm{=} results in

! TeX capacity exceeded, sorry [input stack size=5000].
\bm@command ->
\let \let \let \let \let \let \let \let \let \let \let \let \l...
l.8 \bm{=}
!  ==> Fatal error occurred, no output PDF file produced!


For displaymath or  (inline) there is no such problem.

Compiled using pdflatex version 3.1415926-2.4-1.40.13 (MiKTeX 2.9)

Would be nice not to have to remember about splitting bm every time. Any cure?

• In the case that the whole equation is bold, maybe you should use \boldmath outside the math environment. – Leo Liu Aug 10 '13 at 10:38

To make the whole equation bold:

\documentclass{article}
\usepackage{breqn}

\begin{document}

{\boldmath
\begin{dmath*}[compact]
a + b = c
\end{dmath*}}

\end{document}


For a bold equals sign:

\documentclass{article}
\usepackage{amsmath}
\usepackage{breqn}

% if you still need bm package otherwhere
\let\saveboldsymbol\boldsymbol
\usepackage{bm}
\let\boldsymbol\saveboldsymbol

\begin{document}

\begin{dmath*}[compact]
a + b \boldsymbol{=} c
\end{dmath*}

\end{document}

• I was about to check it but for some reason forgot to do so. It solves my actual problem, so thank you for your answer. Still there is a conflict between bm and breqn which may be troublesome. – Paul Aug 10 '13 at 10:57
• @Paul: Does amsmath's old \boldsymbol solve your problem? – Leo Liu Aug 10 '13 at 10:59
• \boldsymbol{a + b = c} works fine so I guess it does. Are there any restrictions for \boldsymbol? I mean why would I still need bm? – Paul Aug 10 '13 at 11:09
• The spacing of \boldsymbol{a+b=c} is wrong. bm package is rather complex to deal with the spacing problems. There're other features described in the manual of bm package. In your particular example, however, \boldmath is still preferred. – Leo Liu Aug 10 '13 at 11:17
• You're right. I will definetely apply \boldmath as it's all I need for now. Maybe once I get some deeper knowledge on LaTeX I try to fix it, because it looks like just an infinite-loop. Do you think it might be that easy? – Paul Aug 10 '13 at 11:24