Creating different "classes" of labels

Question

I'm trying to write up a paper and I'd like to have a different class of labels for identities vs equations. ie I want something like \label{eq:firsteq} and \label{id:firstid} such that the numbering system for my identities (\ref{id: whatever) is distinct from my numbering system for equations (\ref{eq: whatever}).

For example say I have

\begin{equation}\label{eq:firsteq} a = b \end{equation}

\begin{equation}\label{id:firstid} c = d \end{equation}

Then I want something so that when I call

\ref{eq:firsteq}

\ref{id:firstid}

I get 1 and 1, not 1 and 2. I've tried googling and found something for distinct enumeration of figures under the caption package, but I'm not doing it for figures. Thanks for your help!

Answer 1

What I did here was use \meaning to determine how the equation environment is defined. I then fashioned an identity environment on the same lines, using a different counter, and label format (brackets, not parens).

It becomes the user's responsibility to use the appropriate equation or identity environment.

\documentclass{article}
\usepackage[T1]{fontenc}
\newcounter{identity}
\makeatletter
\newenvironment{identity}
  {$$\refstepcounter{identity}}
  {\eqno\hbox{[\arabic{identity}]}$$\@ignoretrue}
\makeatother
\begin{document}
\meaning\equation

\meaning\endequation

\begin{equation}\label{eq:firsteq} a = b \end{equation}

\begin{identity}\label{id:firstid} c = d \end{identity}

Reference equation \ref{eq:firsteq}.

Reference identity \ref{id:firstid}.
\end{document}