我正在努力改进我的答案并且我找到了一个在 Overleaf 上完美运行的解决方案（我查看了日志，而不仅仅是显示的内容）。
\listfiles
\documentclass[12pt,fleqn]{article}
\usepackage{amsmath}
\usepackage{environ}
\usepackage{tikz}
\usetikzlibrary{matrix}
\usetikzlibrary{decorations.pathreplacing, calligraphy, calc}
\tikzset{
mymatr/.style={
matrix of math nodes,
column sep = 10pt,
nodes={
anchor=text,
inner xsep=3pt
},
inner xsep=7pt,
ampersand replacement=\&
}
}
\NewEnviron{mybrak}[1][2]{%
\begin{tikzpicture}[baseline=(mybase)]
\matrix[mymatr](A){
\BODY\\
};
\coordinate (mybase) at ($(A-1-1.text)!.5! (A-#1-1.text)$);
\draw[thick]([xshift=-6.4pt]A-1-1.west) -- +(4.4pt,0);
\foreach[evaluate=\mystep as \prev using int(\mystep-1)] \mystep in {2,...,#1}{
\draw[thick]([xshift=-6pt]A-\prev-1.west) -- ([xshift=-6pt]A-\mystep-1.west) -- + (4pt,0);
}
\end{tikzpicture}
}
\NewEnviron{mycurly}[1][2]{%
\begin{tikzpicture}[baseline=(mybase)]
\matrix[mymatr](A){
\BODY\\
};
\coordinate (mybase) at ($(A-1-1.text)!.5! (A-#1-1.text)$);
\draw[line width=.9pt,decorate,decoration={calligraphic brace,amplitude=4pt, mirror}](A-1-1.west) -- (A-#1-1.west);
\end{tikzpicture}
}
\begin{document}
Environment who puts curly braces:
\[
\begin{mycurly}
\frac{3}{4}x+y=2 \\
e^{2x}+3y=4
\end{mycurly}
\]
if you have more than 2 equation, you have to indicate their number in the optional argument:
\[
\begin{mycurly}[3]
\frac{3}{4}x+y=2 \\
e^{2x}+3y=4\\
\sqrt{x+3}+5z=0
\end{mycurly}
\]
\[
\begin{mycurly}[4]
x+y=2 \\
2x+3y=4 \\
3x+5z=0 \\
\dfrac{7x}{x+9}+y+z=2
\end{mycurly}
\]
Environment who puts square brakets:
\[
\begin{mybrak}
\frac{3}{4}x+y=2 \\
e^{2x}+3y=4
\end{mybrak}
\]
if you have more than 2 equation, you have to indicate their number in the optional argument:
\[
\begin{mybrak}[3]
\frac{3}{4}x+y=2 \\
e^{2x}+3y=4\\
\sqrt{x+3}+5z=0
\end{mybrak}
\]
\[
\begin{mybrak}[4]
x+y=2 \\
2x+3y=4 \\
3x+5z=0 \\
\dfrac{7x}{x+9}+y+z=2
\end{mybrak}
\]
Please note you have to use \verb|\&| instead of \verb|&| here:
\[
f(x) =
\begin{mycurly}[4]
\dfrac{1}{3}x+y=2 \& \text{if }x<0 \\
2x+3y=4 \& \text{if }0\leq x<1\\
3x+5z=0 \& \text{if }1\leq x<2\\
\dfrac{7x}{x+9}+y+z=2 \& \text{if } x>2
\end{mycurly}
\]
\[
f(x) =
\begin{mycurly}[3]
2x+3y=4 \& \text{if } x<1\\
3x+5z=0 \& \text{if }1\leq x<2\\
\dfrac{7x}{x+9}+y+z=2 \& \text{if } x>2
\end{mycurly}
\]
It works also with the bracket type (even if I don't know if it is used in your country):
\[
f(x) =
\begin{mybrak}[4]
\dfrac{1}{3}x+y=2 \& \text{if }x<0 \\
2x+3y=4 \& \text{if }0\leq x<1\\
3x+5z=0 \& \text{if }1\leq x<2\\
\dfrac{7x}{x+9}+y+z=2 \& \text{if } x>2
\end{mybrak}
\]
\[
f(x) =
\begin{mybrak}[3]
2x+3y=4 \& \text{if } x<1\\
3x+5z=0 \& \text{if }1\leq x<2\\
\dfrac{7x}{x+9}+y+z=2 \& \text{if } x>2
\end{mybrak}
\]
\end{document}
使用以下版本的软件包：
*File List*
article.cls 2014/09/29 v1.4h Standard LaTeX document class
fleqn.clo 2016/12/29 v1.2a Standard LaTeX option (flush left equations)
size12.clo 2014/09/29 v1.4h Standard LaTeX file (size option)
amsmath.sty 2016/11/05 v2.16a AMS math features
amstext.sty 2000/06/29 v2.01 AMS text
amsgen.sty 1999/11/30 v2.0 generic functions
amsbsy.sty 1999/11/29 v1.2d Bold Symbols
amsopn.sty 2016/03/08 v2.02 operator names
environ.sty 2014/05/04 v0.3 A new way to define environments
trimspaces.sty 2009/09/17 v1.1 Trim spaces around a token list
tikz.sty 2015/08/07 v3.0.1a (rcs-revision 1.151)
pgf.sty 2015/08/07 v3.0.1a (rcs-revision 1.15)
pgfrcs.sty 2015/08/07 v3.0.1a (rcs-revision 1.31)
everyshi.sty 2001/05/15 v3.00 EveryShipout Package (MS)
pgfrcs.code.tex
pgfcore.sty 2010/04/11 v3.0.1a (rcs-revision 1.7)
graphicx.sty 2017/06/01 v1.1a Enhanced LaTeX Graphics (DPC,SPQR)
keyval.sty 2014/10/28 v1.15 key=value parser (DPC)
graphics.sty 2017/06/25 v1.2c Standard LaTeX Graphics (DPC,SPQR)
trig.sty 2016/01/03 v1.10 sin cos tan (DPC)
graphics.cfg 2016/06/04 v1.11 sample graphics configuration
pdftex.def 2017/06/24 v1.0g Graphics/color driver for pdftex
pgfsys.sty 2014/07/09 v3.0.1a (rcs-revision 1.48)
pgfsys.code.tex
pgfsyssoftpath.code.tex 2013/09/09 (rcs-revision 1.9)
pgfsysprotocol.code.tex 2006/10/16 (rcs-revision 1.4)
xcolor.sty 2016/05/11 v2.12 LaTeX color extensions (UK)
color.cfg 2016/01/02 v1.6 sample color configuration
pgfcore.code.tex
pgfcomp-version-0-65.sty 2007/07/03 v3.0.1a (rcs-revision 1.7)
pgfcomp-version-1-18.sty 2007/07/23 v3.0.1a (rcs-revision 1.1)
pgffor.sty 2013/12/13 v3.0.1a (rcs-revision 1.25)
pgfkeys.sty
pgfkeys.code.tex
pgfmath.sty
pgfmath.code.tex
pgffor.code.tex
tikz.code.tex
spath3.sty 2016/02/19 v1.1 Functions for manipulating PGF soft paths
expl3.sty 2017/05/29 L3 programming layer (loader)
expl3-code.tex 2017/05/29 L3 programming layer
l3pdfmode.def 2017/03/18 v L3 Experimental driver: PDF mode
xparse.sty 2017/05/29 L3 Experimental document command parser
supp-pdf.mkii
epstopdf-base.sty 2016/05/15 v2.6 Base part for package epstopdf
infwarerr.sty 2016/05/16 v1.4 Providing info/warning/error messages (HO)
grfext.sty 2016/05/16 v1.2 Manage graphics extensions (HO)
kvdefinekeys.sty 2016/05/16 v1.4 Define keys (HO)
ltxcmds.sty 2016/05/16 v1.23 LaTeX kernel commands for general use (HO)
kvoptions.sty 2016/05/16 v3.12 Key value format for package options (HO)
kvsetkeys.sty 2016/05/16 v1.17 Key value parser (HO)
etexcmds.sty 2016/05/16 v1.6 Avoid name clashes with e-TeX commands (HO)
ifluatex.sty 2016/05/16 v1.4 Provides the ifluatex switch (HO)
pdftexcmds.sty 2017/03/19 v0.25 Utility functions of pdfTeX for LuaTeX (HO)
ifpdf.sty 2017/03/15 v3.2 Provides the ifpdf switch
epstopdf-sys.cfg 2010/07/13 v1.3 Configuration of (r)epstopdf for TeX Live
***********
但是如果我在我的计算机上尝试使用更新版本的软件包：
*File List*
article.cls 2014/09/29 v1.4h Standard LaTeX document class
fleqn.clo 2016/12/29 v1.2a Standard LaTeX option (flush left equations)
size12.clo 2014/09/29 v1.4h Standard LaTeX file (size option)
amsmath.sty 2017/09/02 v2.17a AMS math features
amstext.sty 2000/06/29 v2.01 AMS text
amsgen.sty 1999/11/30 v2.0 generic functions
amsbsy.sty 1999/11/29 v1.2d Bold Symbols
amsopn.sty 2016/03/08 v2.02 operator names
environ.sty 2014/05/04 v0.3 A new way to define environments
trimspaces.sty 2009/09/17 v1.1 Trim spaces around a token list
tikz.sty 2015/08/07 v3.0.1a (rcs-revision 1.151)
pgf.sty 2015/08/07 v3.0.1a (rcs-revision 1.15)
pgfrcs.sty 2015/08/07 v3.0.1a (rcs-revision 1.31)
everyshi.sty 2001/05/15 v3.00 EveryShipout Package (MS)
pgfrcs.code.tex
pgfcore.sty 2010/04/11 v3.0.1a (rcs-revision 1.7)
graphicx.sty 2017/06/01 v1.1a Enhanced LaTeX Graphics (DPC,SPQR)
keyval.sty 2014/10/28 v1.15 key=value parser (DPC)
graphics.sty 2017/06/25 v1.2c Standard LaTeX Graphics (DPC,SPQR)
trig.sty 2016/01/03 v1.10 sin cos tan (DPC)
graphics.cfg 2016/06/04 v1.11 sample graphics configuration
pdftex.def 2018/01/08 v1.0l Graphics/color driver for pdftex
pgfsys.sty 2014/07/09 v3.0.1a (rcs-revision 1.48)
pgfsys.code.tex
pgfsyssoftpath.code.tex 2013/09/09 (rcs-revision 1.9)
pgfsysprotocol.code.tex 2006/10/16 (rcs-revision 1.4)
xcolor.sty 2016/05/11 v2.12 LaTeX color extensions (UK)
color.cfg 2016/01/02 v1.6 sample color configuration
pgfcore.code.tex
pgfcomp-version-0-65.sty 2007/07/03 v3.0.1a (rcs-revision 1.7)
pgfcomp-version-1-18.sty 2007/07/23 v3.0.1a (rcs-revision 1.1)
pgffor.sty 2013/12/13 v3.0.1a (rcs-revision 1.25)
pgfkeys.sty
pgfkeys.code.tex
pgfmath.sty
pgfmath.code.tex
pgffor.code.tex
tikz.code.tex
spath3.sty 2016/02/19 v1.1 Functions for manipulating PGF soft paths
expl3.sty 2018-11-19 L3 programming layer (loader)
expl3-code.tex 2018-11-19 L3 programming layer
l3pdfmode.def 2018-11-19 v L3 Experimental driver: PDF mode
xparse.sty 2018-10-17 L3 Experimental document command parser
supp-pdf.mkii
epstopdf-base.sty 2016/05/15 v2.6 Base part for package epstopdf
infwarerr.sty 2016/05/16 v1.4 Providing info/warning/error messages (HO)
grfext.sty 2016/05/16 v1.2 Manage graphics extensions (HO)
kvdefinekeys.sty 2016/05/16 v1.4 Define keys (HO)
ltxcmds.sty 2016/05/16 v1.23 LaTeX kernel commands for general use (HO)
kvoptions.sty 2016/05/16 v3.12 Key value format for package options (HO)
kvsetkeys.sty 2016/05/16 v1.17 Key value parser (HO)
etexcmds.sty 2016/05/16 v1.6 Avoid name clashes with e-TeX commands (HO)
ifluatex.sty 2016/05/16 v1.4 Provides the ifluatex switch (HO)
pdftexcmds.sty 2018/09/10 v0.29 Utility functions of pdfTeX for LuaTeX (HO)
ifpdf.sty 2018/09/07 v3.3 Provides the ifpdf switch
epstopdf-sys.cfg 2010/07/13 v1.3 Configuration of (r)epstopdf for TeX Live
***********
我收到错误（随后收到许多其他错误）：
! Undefined control sequence.
<argument> \g__prg_map_int
l.54 \end{mycurly}
该错误似乎出在calligraphyTikZ 的库中，但自 2016/02/19 以来它一直没有改变。
我该如何解决这个错误？
答案1
在收紧某些概念的过程中expl3，删除了一些内部命令。在这里，一个命令被第三方软件包使用。（收紧的部分原因是不清楚第三方是否不应使用此代码，因此软件包作者没有错。）在那里的代码被修改之前，人们可以使用
\usepackage{expl3}
\ExplSyntaxOn
\int_new:N \g__prg_map_int
\ExplSyntaxOff
前
\usetikzlibrary{decorations.pathreplacing, calligraphy, calc}