equationsnumbering
I just read a book where the equations in the Introduction were numbered slightly differently compared to the other sections, namely by (In.x) where x stands for the number (so it starts off as (In.1), (In.2), (In.3) and so on.
I'd like to try this this but I haven't found out so far how to do this systematically, i.e. not tagging each equation manually but rather using someting like the \label functionality .. any suggestions?
Assuming that these numbered quote environments are at the top level and not nested in other list environments, you can exploit the fact that, unless your equation numbers are too wide, they will fit in the available white space; in case they are wider for fitting, you should redefine quote in the first place.
\documentclass{article}
\usepackage{blindtext}
\newsavebox\ideabox
\newenvironment{idea}
{\begin{equation}
\begin{lrbox}{\ideabox}
\begin{minipage}{\dimexpr\columnwidth-2\leftmargini}
\setlength{\leftmargini}{0pt}%
\begin{quote}}
{\end{quote}
\end{minipage}
\end{lrbox}\makebox[0pt]{\usebox{\ideabox}}
\end{equation}}
\begin{document}
\begin{quote}\blindtext\end{quote}\begin{equation}E=mc^2\end{equation}
\begin{idea}
\blindtext
\end{idea}
\end{document}
The “equationed” quote is typeset in a zero width box, so the equation number will not force a shift to the left.
Let’s see if I guessed correctly what you wish to get:
This output was generated by the following code:
% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly
% declare the paper format.
\usepackage[T1]{fontenc} % Not always necessary, but recommended.
% End of standard header. What follows pertains to the problem at hand.
\usepackage{amsmath}
\numberwithin{equation}{section}
\newcommand*{\myTagFormat}[2]{(\ref{#1})($#2$)}
\begin{document}
\section{First}
Just to include a couple of equations:
\begin{align}
1 &= 1 \label{eq:one} \\
1+2 &= 3 \label{eq:two}
\end{align}
Until now, we have equations \eqref{eq:one} and~\eqref{eq:two}.
\section{Second}
Still another equation of the same form:
\begin{equation}
1+2+3 = 6 \label{eq:three}
\end{equation}
Generalizing equations \eqref{eq:one}, \eqref{eq:two}, and~\eqref{eq:three}, we
claim that
% Little trick:
\refstepcounter{equation}\label{eq:base}% <-- Note!
\begin{equation}
1+2+\dots+n = \frac{n(n+1)}{2}
\tag*{\myTagFormat{eq:base}{n}}\label{eq:base-n}
\end{equation}
Now you can either:
\begin{itemize}
\item
reference equation~\ref{eq:base-n} directly (note that you must use
\verb|\ref| instead of \verb|\eqref|, here), or
\item
say that equation~\myTagFormat{eq:base}{i+1} follows from
equation~\myTagFormat{eq:base}{i} by adding $i+1$ on both sides of the
latter.
\end{itemize}
One more equation to check that we haven't spoiled the numbering:
\begin{equation}
x=y
\end{equation}
\end{document}
Best Answer
You can do this using
If you want to switch it back, you can use
A complete MWE follows.