1

After some helpful responses, what I have is below:

But I would like the equation now numbered with (1.2a) to be (1.2); the equation now numbered (1.2b) to be (1.3); and the equation now numbered (1.2c) to be (1.4); and the equation now numbered (1.3) to be (1.5)

\documentclass{article}
\usepackage{amsmath}
\usepackage{hyperref}

\usepackage{lipsum} % for mock text

\renewcommand{\theequation}{\thesection.\arabic{equation}}


\begin{document}


\section{First section} 

    An equation here:
        \begin{equation} \label{x=y} 
    x = y 
    \end{equation}

    and the main one here:


    \begin{subequations}\label{main}
        \begin{equation}
        \left.
        \addtocounter{equation}{-1}
        \edef\theHparentequation{x.\theHparentequation}
        \begin{minipage}{0.8\displaywidth}
        \vspace*{-\baselineskip}
        \begin{align}
        a&=b \label{a} \\
        c&=d \label{b} \\
        e&=f \label{c}
        \end{align}
        \end{minipage}
        \right\}
        \label{main} \tag{MAIN}  
        \end{equation} 
    \end{subequations}

    References: \eqref{main}; \eqref{a}; \eqref{b}; \eqref{c}.


    Another equation here:
    \begin{equation} \label{u=v}  
    u = v  
    \end{equation}


\end{document}
  • 1
    Admittedly not with a curly bracket, but probably you are interested in something like \documentclass{article} \usepackage{amsmath} \usepackage{hyperref} \begin{document} \begin{subequations} \begin{equation} a=b \label{first} \end{equation} \begin{equation} c=d \end{equation} \begin{equation} e=f \end{equation} \end{subequations} \eqref{first} \end{document}. – leandriis Feb 18 at 20:46
  • 2
    Similar logic, different looks: tex.stackexchange.com/questions/163548 – Dr. Manuel Kuehner Feb 18 at 21:10
  • Thanks, sort of, but not quite. The MAIN-EQ-NO should be really different from the other equation numbers. And there should be a tag for the MAIN-EQ-NO, it should not be just a number. And I would want to reference MAIN-EQ-NO in the text. – district9 Feb 18 at 22:11
  • I added an answer, but a simpler subequations environment is much easier and readers will understand the references very clearly. – egreg Feb 20 at 18:19
2

Maybe something of this kind, but the brace and the main equation number are unnecessary, in my opinion.

\documentclass{article}
\usepackage{amsmath}
\usepackage{hyperref}

\usepackage{lipsum} % for mock text

\begin{document}

\lipsum[2]
\begin{subequations}\label{main}
\begin{equation}
\left.
\addtocounter{equation}{-1}
\edef\theHparentequation{x.\theHparentequation}
\begin{minipage}{0.8\displaywidth}
\vspace*{-\baselineskip}
\begin{align}
a&=b \label{a} \\
c&=d \label{b} \\
e&=f \label{c}
\end{align}
\end{minipage}
\right\}
\tag{\ref*{main}}
\end{equation}
\end{subequations}
\lipsum[3]

References: \eqref{main}; \eqref{a}; \eqref{b}; \eqref{c}.

\end{document}

enter image description here

Without subequations, it is similar, but I think it's a bad idea as well as the one in the other answer: just using subequation would suffice.

\documentclass{article}
\usepackage{amsmath}
\usepackage{hyperref}

\usepackage{lipsum} % for mock text

\numberwithin{equation}{section}


\begin{document}

\section{A title}

\lipsum[1][1-2]
\begin{equation}
x=y
\end{equation}

\lipsum[2][1-4]
\begin{equation}
\left.
\begin{minipage}{0.8\displaywidth}
\addtocounter{equation}{-1}
\renewcommand{\theHequation}{x\theequation}
\vspace*{-\baselineskip}
\begin{align}
a&=b \label{a} \\
c&=d \label{b} \\
e&=f \label{c}
\end{align}
\end{minipage}
\right\}
\tag{MAIN}\label{main}
\end{equation}
\lipsum[3][1-3]

References: \eqref{main}; \eqref{a}; \eqref{b}; \eqref{c}.

\end{document}

enter image description here

With just subequations:

\documentclass{article}
\usepackage{amsmath}
\usepackage{hyperref}

\usepackage{lipsum} % for mock text

\numberwithin{equation}{section}


\begin{document}

\section{A title}

\lipsum[1][1-2]
\begin{equation}
x=y
\end{equation}

\lipsum[2][1-4]
\begin{subequations}\label{main}
\begin{align}
a&=b \label{a} \\
c&=d \label{b} \\
e&=f \label{c}
\end{align}
\end{subequations}
\lipsum[3][1-3]

References: \eqref{main}; \eqref{a}; \eqref{b}; \eqref{c}.

\end{document}

enter image description here

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