例子：
\documentclass[10pt]{beamer}
\usetheme{Singapore}
\setbeamertemplate{navigation symbols}{}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{helvet}
\usepackage{natbib}
\usepackage{graphicx}
\usepackage{amssymb}
\usepackage{textcomp}
\usepackage{marvosym}
\usepackage{multicol}
\usepackage[version=3]{mhchem}
\usepackage{siunitx}
\usepackage{chemfig}
\mode<presentation>
\begin{document}
\begin{frame}
\frametitle{}
\chemname[2ex]{\chemfig{H-[, 0.5]C(-[2, 0.5]H)(-[6, 0.5]H)-C(=[1]O)(-[7]O-[,,,,red]H)}}{\textcolor{red}{ethanoic acid}} \chemsign{+} \chemname[2ex]{\chemfig{H-[, 0.5]C(-[2, 0.7]H)(-[6, 0.5]H)-C(-[2, 0.5]H)(-[6, 0.5]H)(-O-[,,,,blue]H)}}{\textcolor{blue}{ethanol}}
\end{frame}
\end{document}
/usr/share/doc/texlive-doc/generic/chemfig/chemfig_doc_en.pdf
错误：
(/usr/local/share/texmf/tex/latex/chemgreek/chemgreek/chemgreek.sty
(/usr/share/texlive/texmf-dist/tex/latex/l3packages/xparse/xparse.sty))
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!
! LaTeX error: "kernel/command-not-defined"
!
! Control sequence \regex_match:NnTF undefined.
!
! See the LaTeX3 documentation for further information.
!
! For immediate help type H <return>.
!...............................................
l.53 ...nerate_variant:Nn \regex_match:NnTF { NV }
?
从其他网页：最新的 MiKTex 更新与 fontspec 不兼容
尝试过并收到同样的错误。
系统：Debian 9。软件包是手动安装的；tlgr 是不是用过的。
要删除什么以及如何删除以恢复到以前的安装？
谢谢。