# Alternative equation numbers

Suppose I have equations that I consider "assumptions" and I want those particular equations to be labelled separately from the others. Specifically, I would like the first assumption to be labelled (A1), the second to be labelled (A2), while the first non-assumption equation will be labelled (1), the second, (2), and so on. Is there a way to do this without having to tag the assumptions individually?

• Yes, with \newtagform that comes with mathtools. – user121799 Jun 23 '18 at 1:57
• @marmot - \newtagform and \usetagform will indeed let the user create equation "numbers" of the form "A1", "A2", etc. However, elsewhere in the document, cross-references to the "assumption equations" will come out as "1", "2", etc if the OP has switched back to the default tag form. – Mico Jun 23 '18 at 9:09

You could set up a custom environment called aequation (short for "assumption equation", I suppose). It behaves mostly like an unnumbered display-equation environment, except that it automatically provides "tags", such as A1 and A2, which can be referenced elsewhere in the document via the usual cross-referencing methods.

\documentclass{article}
\usepackage{amsmath}   % for "\tag" macro
\newcounter{aequation} % "assumption-equation" counter
\newenvironment{aequation}{%
$\refstepcounter{aequation}% \tag{A\arabic{aequation}}% tag: "A" prefix and counter }{$}

\usepackage[colorlinks]{hyperref} % just for this example
\usepackage[noabbrev]{cleveref}   % just for this example

\begin{document}
\begin{aequation} \label{eq:a}  1+1=2\end{aequation}%
\begin{aequation} \label{eq:e}  d+e=f\end{aequation}%
$$\label{eq:b} 2+2=4$$
\begin{aequation} \label{eq:c}  0+0=0\end{aequation}%
$$\label{eq:d} a+b=c$$

Cross-references to \eqref{eq:a}, \eqref{eq:b}, \eqref{eq:c}, and \eqref{eq:d}.

Cross-references to assumptions \labelcref{eq:a,eq:c} and to \cref{eq:b,eq:d}.
\end{document}