KTUGFaq
KTUG FAQ
Deprive a mirror of its silver and even the Czar won't see his face.
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iftex package ¶
\usepackage{iftex}
\ifPDFTeX ... \else ... \fi
\ifXeTeX ... \else ... \fi
\ifLuaTeX ... \else ... \fi
\RequirePDFTeX \RequireXeTeX \RequireLuaTeX