[texhax] Re-using equation numbers

[Robin Fairbairns]

> The following is a numbered equation in an early chapter of a thesis
> \begin{equation}
> \mathrm{\dot{H} + O_2  \rightarrow  \dot{O}H + O }
> \label{key}
> \end{equation}
> 
> We want to re-use the equation number in a restatement of the
> equation  many pages on from the first statement because the reader
> may well have forgotten what it referred to ...
> 
> Is there a better or more elegant solution than this?
> 
> $$
> \mathrm{\dot{H} + O_2 \rightarrow \dot{O}H + O }  \rule{25pt}{0pt}
> \eqref{key}
> $$
> 
> in LaTeX + Amsmath

don't use $$ in amsmath; use the amsmath \tag command:

\[ \mathrm{\dot{H} + O_2 \rightarrow \dot{O}H + O } \tag{\eqref{key}} \]

robin