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style="font-family: Lucida Sans;">Hello,<br><br>Here is a small file 
that used to work but doesn't anymore:<br><br>\input eplain<br>\beginpackages<br>\usepackage{color}<br>\endpackages
 <br>\long\def\red#1{{\color{red}#1}}<br>\red{ab}<br>\bye<br><br><br>The
 error message is:<br><br>This is pdfTeX, Version 
3.141592653-2.6-1.40.24 (TeX Live 2022) (preloaded format=pdftex)<br> restricted
 \write18 enabled.<br>entering extended mode<br>(./essai.tex 
(/usr/local/texlive/2022/texmf-dist/tex/eplain/eplain.tex)<br>(/usr/local/texlive/2022/texmf-dist/tex/plain/graphics-pln/miniltx.tex)<br>(/usr/local/texlive/2022/texmf-dist/tex/latex/graphics/color.sty<br>(/usr/local/texlive/2022/texmf-dist/tex/latex/graphics-cfg/color.cfg)<br>(/usr/local/texlive/2022/texmf-dist/tex/latex/graphics-def/pdftex.def)<br>(/usr/local/texlive/2022/texmf-dist/tex/latex/graphics/mathcolor.ltx<br>/usr/local/texlive/2022/texmf-dist/tex/latex/graphics/mathcolor.ltx:21:
 Undefined control sequence.<br>l.21 \ExplSyntaxOn<br><br>Many thanks 
for help.<br>Regards,<br><br>Gérald<br></div></body></html>