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In the template of Proceedings of the Royal Society A, I want to use the command "\Deltaup", however, compiling the file, I encounter the following error: "Undefined control sequence. $\Deltaup". I would like to know how can I resolve this problem. Thank you! The template starts as follows:

\documentclass[]{rsos}%%%%where rsos is the template name

%%%% *** Do not adjust lengths that control margins, column widths, etc. *** \usepackage{upgreek}

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  • Welcome to tex.sx. The default \Delta is upright, as are all uppercase Greek letters. The package upgreek also makes the lowercase letters upright. Apr 28, 2023 at 1:59
  • Thank you BarBara. However, what you mentioned is not the case for me. I mean in the template I mentioned, \Delta does not correspond to the upright capital Delta which I need, but it produces italic capital Delta. In addition, the package upgreek does not fix this problem. I used \Deltaup, but it causes the error I mentioned in my question. I would like to know if there is any trick to resolve this problem and to be able to produce the upright capital \Delta. Thank you.
    – Rayan
    Apr 28, 2023 at 2:27
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    It's not easy to find the document class! (But I did.) It contains an option CapsGreek which, if set, resets all uppercase Greek to italic, and then executes it. But it doesn't actually make the change until \AtBeginDocument. So it might be possible to save the upright Delta for later use before that happens. Using your suggested name, add this line before \begin{document}: \let\Deltaup\Delta. Not tested. (It's past my time to go to sleep.) Apr 28, 2023 at 3:13
  • Dear Barbara, thank you so much for your time and your help.
    – Rayan
    Apr 28, 2023 at 3:30
  • Your suggestion worked. Thanks again.
    – Rayan
    Apr 28, 2023 at 3:31

1 Answer 1

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The PRSA document class (rsproca_new.cls) contains an option Capsgreek that, if set, specifies that all uppercase Greek will be italic. In the case of \Delta, this is set up through \let\Delta\varDelta, making it impossible to use \Delta in its original meaning.

Capsgreek is "executed" (set up) automatically, but not activated until \AtBeginDocument making it possible to preserve the original meaning of the capital Greek letters if they are caught before the transformation occurs, i.e., before AtBeginDocument.

You have suggested the name \Deltaup for the upright delta. Using this name, you can save the upright Delta for later use by adding this line before \begin{document}:

\let\Deltaup\Delta

The same mechanism can be used to "preserve" the other uppercase Greek letters that are normally defined, remembering that the Greek caps that have the same shape as Latin uppercase letters do not have defined TeX command names.

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