Because I don't like that Euler calligraphic script provided by Latin Modern
Math, I want to revert
to Computer Modern for the uppercase calligraphic letters.
I don't have access to a context installation right now so cannot give a
more detailed answer.
But typically math fonts provide two stylistic sets of caligraphic
letters: one similar to the default \mathcal alphabel and the other
similar to \mathscr alphabet (RSFS fonts etc.) The latter is the default,
but typically moving to the traditional mathcal styled calligraphic
letters should be as simple as setting an appropriate font feature.
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