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Suppose I take the variable $X_a$ and square it. To be clear, the _a is part of the variable's name, whereas the ^2 will denote the mathematical operation of squaring.

I could typeset this as

  • $X_a^2$
  • $X_a{}^2$
  • $(X_a)^2$

Is there an accepted convention about which approach is best?

closed as primarily opinion-based by user156344, Raaja, Stefan Pinnow, Mensch, TeXnician Mar 4 at 11:43

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    The most normal one is probably the first. Two is uncommon in the fields I work with. Third would probably be best if you are afraid your readers will not understand the first type – daleif Nov 30 '18 at 15:18
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    I’d also go for either the first or the third choice. The final choice should depend importantly on what exactly X_a denotes. Are there also variables named X_b, X_c, etc? Incidentally, if X_a were an n-tupel, I would write its inner product as {X_a}’X_a, to make sure that the transpose symbol is not placed directly above the letter a. – Mico Nov 30 '18 at 16:17