Number codes for cyrillic letters

Question

The command

\DeclareMathSymbol{\sha}{\mathalpha}{cyrletters}{"58}

produces the russian letter Sha (III)

Which number do I have to replace 58 with in order to get the labial b?

Answer 1

With unicode-math, use the Unicode value (I think "0411) or just type in the letter.

With a legacy 8-bit font, look up the T2A encoding chart in Appendix A.1 of The LaTeX Font Encoding Guide.

With either of these, you could load your Cyrillic text font, then use something like \newcommand\mathBe{\mathord{\textnormal{Б}}}. (You might actually prefer to inherit \bfseries from the surrounding text, for chapter or section headings. If so, use \textup or \textit instead of \textnormal.) You could also type in ^^^^0411, which always means the Unicode codepoint U+0411 regardless of the current font encoding, instead of Б. With fontspec or unicode-math, this is set up for you. In legacy NFSS mode, you’d need to load \usepackage[T2A, T1]{fontenc} and load a font package that supports Cyrillic. (UTF-8 input is now the default in LaTeX.)

With the even older AMS Cyrillic font, check out the amsfonts documentation (As Steven B. Segletes said in his comment.)