# How can I use the AMS Euler font in plain TeX?

I want to use the AMS Euler font designed by Zapf in my document. I looked for packages on CTAN (e.g., the euler package), but they are specifically designed for LaTeX.

I took a look at the gkpmac.tex file Knuth wrote from Concrete Mathematics and it is likely to contain the answer I am looking for, but I can't fully understand it and determine what lines to extract to an eumac.tex or euler.tex file (I don't know what the naming convention is in that case).

I found this document, User's Guide to AMSFonts Version 2, https://texdoc.org/serve/amsfndoc.pdf/0, which helped guide the plain TeX implementation. See section 5.1 on pp. 12-13.

In the MWE, I activate the fraktur and roman euler fonts, in both medium and bold. Other euler font families (eusm, eusb, and euex) should follow the same approach, with different supported sizes for euex.

\input amssym
%\input amssym.def

\font\teneufm=eufm10
\font\seveneufm=eufm7
\font\fiveeufm=eufm5
\newfam\eufmfam
\textfont\eufmfam=\teneufm
\scriptfont\eufmfam=\seveneufm
\scriptscriptfont\eufmfam=\fiveeufm
\def\eufm#1{{\fam\eufmfam\relax#1}}

\font\teneufb=eufb10
\font\seveneufb=eufb7
\font\fiveeufb=eufb5
\newfam\eufbfam
\textfont\eufbfam=\teneufb
\scriptfont\eufbfam=\seveneufb
\scriptscriptfont\eufbfam=\fiveeufb
\def\eufb#1{{\fam\eufbfam\relax#1}}

\font\teneurm=eurm10
\font\seveneurm=eurm7
\font\fiveeurm=eurm5
\newfam\eurmfam
\textfont\eurmfam=\teneurm
\scriptfont\eurmfam=\seveneurm
\scriptscriptfont\eurmfam=\fiveeurm
\def\eurm#1{{\fam\eurmfam\relax#1}}

\font\teneurb=eurb10
\font\seveneurb=eurb7
\font\fiveeurb=eurb5
\newfam\eurbfam
\textfont\eurbfam=\teneurb
\scriptfont\eurbfam=\seveneurb
\scriptscriptfont\eurbfam=\fiveeurb
\def\eurb#1{{\fam\eurbfam\relax#1}}

$$\eufm{XYZ} = \eufb{XYZ} = \eurm{xyz} = \eurb{xyz}$$
\bye


• Thank you for your answer, however I don't understand why you are importing the amssym.def file since you are writing the definitions below Oct 5 at 21:41
• @Laravel It is because I stumbled into the answer piecemeal (and don't work often in Plain TeX). Thanks for letting me know. Oct 5 at 21:42
• No problem, thanks again Oct 5 at 21:45