I have an equation like:
\begin{equation} \label{whatever}
x+y=1
\end{equation}
I want to write it again, keeping the same number. I know I could do the following:
\begin{equation}
x+y=1 \tag{\ref{whatever}}
\end{equation}
However, I would like to get the same outcome without rewriting the full equation. The reason is that I may change the first equation, and I would like the change to be automatically applied to all the cases in which the equation is repeated. I.e. I'd like to have something like
\begin{equation}
\rewrite{whatever} \tag{\ref{whatever}}
\end{equation}
Is it possible?
