# Plain TeX bold math in section titles

I apologize if this question is very similar to others, but the other solutions have not worked for me. I am using plain TeX, and trying to make the math in my section titles bold. Any help would be greatly appreciated.

• Welcome to TeX.SX! Instead of just stating that other solutions didn't work for you, it would be better to also show what you have tried. – siracusa Sep 10 at 1:29

Set up the math fonts for the bold version.

\font\tenib=cmmib10
\font\sevenib=cmmib7
\font\fiveib=cmmib5
\font\tensyb=cmbsy10
\font\sevensyb=cmbsy7
\font\fivesyb=cmbsy5
\font\tenexb=cmexb10

\def\boldmath{%
\textfont0=\tenbf \scriptfont0=\sevenbf \scriptscriptfont0=\fivebf
\textfont1=\tenib \scriptfont1=\sevenib \scriptscriptfont1=\fiveib
\textfont2=\tensyb \scriptfont2=\sevensyb \scriptscriptfont2=\fivesyb
\textfont3=\tenexb \scriptfont3=\tenexb \scriptscriptfont3=\tenexb
}

\catcode@=11
\outer\def\beginsection#1\par{\vskip\z@ plus.3\vsize\penalty-250
\vskip\z@ plus-.3\vsize\bigskip\vskip\parskip
\message{#1}\leftline{\bf\boldmath#1}\nobreak\smallskip\noindent}
\catcode@=12

Some text and a formula $a+\sum_i a_i\otimes c$

\beginsection Some text and a formula $a+\sum_i a_i\otimes c$

Some text and a formula $a+\sum_i a_i\otimes c$

\bye • Argh: \outer!!! – Joseph Wright Sep 10 at 8:37
• @JosephWright Would you dispute Knuth's authority? ;-) – egreg Sep 10 at 8:44
• Hans introduced \frozen in LuaMetaTeX. That's going to be the new \outer. – Henri Menke Sep 10 at 8:47
• Knuth did provide \pmb on page 386 of the TeXbook. It's not part of TeX or even listed in the index (except under boldface). – John Kormylo Sep 10 at 16:30
• @JohnKormylo That's only for real emergencies. – egreg Sep 10 at 17:03