# Typesetting a variable which has both accent and subscript

How to typeset a variable like:

Whether do I write $\hat{A}\vphantom{A}_0$ or simply write $\hat{A}_0$? (I had seen the former in a template).

BTW, what about $f'^2$? Is $f^{\prime2}$ or $f^{\prime\,2}$ or ${f^{\prime}}^2$ or $f^{\prime}\vphantom{f}^2$?

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Just $\hat{A}_0$ is OK. \vphantom is even harmful, for some letter like I.
@L.L. What about $f'^2$? Is $f^{\prime2}$ or $f^{\prime\,2}$ or ${f^{\prime}}^2$ or $f^{\prime}\vphantom{f}^2$? –  Stufazi Hoqckt Apr 23 '11 at 8:53
I think (f')^2 is better. –  Leo Liu Apr 23 '11 at 15:55