To insert text in mathmode, there are a couple of commands:
\mathrmfor Roman script,
\mathbffor bold weight,
\mathitfor italic shape,
\mathsffor the sans serif variant,
and so on. Now, sometimes I would like to have some math entities typeset upright (see for example How to best typeset "special" constants (complex unit i, Euler's number e,...)?).
I understand that
\mathrm sets the text in Roman and upright, but in some cases I do not want serifs (e.g., in presentations). The command
\mathup does not seem to exist.
What is recommended way to set upright text in math mode?