I'd like to write all mathematical constants (this includes some Greek letters) in upright style – here on Stack Exchange (math mode). Is it possible to write an upright pi, for example? If so, how to do that?
It bothers me pretty much, since, in any document (also math answers, questions...), either all constants should be upright, or no constants should be upright.
For some reason,
\mathrm works for Latin alphabet but not for Greek alphabet.