Can someone tell me what is going on here?



An inline equation $\cal{A}\subseteq \{0,\dots,n\}\times \{0,\dots,m\}$
with funny characters instead of numbers.


Instead of 0, n and m, a backslash, an updownarrow and another symbol are typeset.


You're using the wrong syntax: the old editions of the LaTeX manual specified that the font change had to be typed

{\cal A}

rather than


because \cal had a behavior quite similar to \it or \bf. However, these commands have been deprecated since the release of LaTeX2e in 1994.

The two letter font changing commands (\it, \bf and so on) and \cal have been replaced by clearer commands with an argument, distinguishing between "text" and "math":

  • {\bf X}\textbf{X} or \mathbf{X}
  • {\it X}\textit{X} or \mathit{X}
  • ...
  • {\cal X}\mathcal{X}

However, for backward compatibility, the old commands are still available (the two letter ones might not be, though, for instance in the memoir class).

Since \cal is a font switching command similar to \it, it influences all the formula; for technical reasons, its result is not readily predictable when non uppercase letters are involved.

Never use \cal, it has been obsolete and deprecated for almost twenty years.

  • @lenz: A lot of the old font commands are switches rather than macros. We tend to see many newcommers write e.g. \Large{text} ... – daleif Jun 26 '13 at 7:59
  • Thanks for the clarification; despite having used (xela)tex for quite some time now, I don't really overlook the layers of commands from different eras. Often, I'm simply led by the autocompletion suggestions of my editor (not in the case of \cal though, that was my own vague guess from the back of my head). – lenz Jun 26 '13 at 9:43
  • @daleif: Yes, sure, you can't blame them for that :-p – lenz Jun 26 '13 at 9:47

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