[texhax] "variablke" formula numbers (in latex)

[Victor Ivrii]

I have a formula which is given by equation say
\begin{equation}
x_\pm = .....
\end{equation}
and which I would like to call $(6.7)_\pm$. Sometimes
I will refer to $(6.7)_\pm$ and sometimes to $(6.7)_+$,
or $(6.7)_-$. Is there a way to do it in the usual
\label - \ref way completely avoiding typing (6.7)?
Also I want it to be consistent with hyperref package

Thank you in advance
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Victor Ivrii, Department of Mathematics, University of Toronto