# Repeat a previously labelled equation without changing the label [duplicate]

Somewhere in my document I have some equation:

$$\label{some_equation} ...$$


I would like to repeat this equation later (so that the reader does not have to flip back and forth between sections), but would like it to appear with the same label (e.g. if it was numbered as equation (1), I would like its "clone" to also appear with the numbering (1)). Is there an easy way to do this?

You could use \tag together with a \label and \ref combo as in the following MWE

\documentclass{article}
\usepackage{amsmath,amssymb}
\usepackage{lipsum}
\pagestyle{empty}
\begin{document}

$$y = x^2 +3 \label{eqn:1}$$

\lipsum[1]

$$y = x^2 +3 \tag{\ref{eqn:1}}$$

\end{document}

• Please, don't use align for one line displays. Ever. – egreg Jul 20 '13 at 19:52