In latex, an equation inside \bf
is in regular font. Exported to TeXmacs, it will be in bold font.
For example, save the following in a TeX file
\documentclass{article}
\begin{document}
\bf The point $x=\infty$
\end{document}
When compiled in LaTeX, the equation is in regular font. Please see texlive.net
When imported to TeXmacs, the equation is in bold font.