Hello good people of Emacs!

To insert unicode math symbols I use TeX input method. This way I get unicode character by typing \Bbb{R}, by typing \Bbb{N}, by typing \Bbb{Z}, etc...

I'm unable to get symbol , since typing \Bbb{Q} does not insert unicode character.

Any Ideas what can be the source of this error?

  • 1
    If it helps the code point is 211A, so it can be entered via C-x 8 RET 211A. The TeX input method covers N, P, R and Z, but not the Q nor C which are in the 10646 character set. See emacs.stackexchange.com/q/3104/2710 which may help with how to extend the input method. Feb 21, 2016 at 13:18
  • @AndrewSwann: Please consider posting your comment as an answer (which can be accepted, so the question is not left "unanswered").
    – Drew
    Feb 21, 2016 at 22:54
  • @Drew OK done, but this is very close to being a duplicate. Feb 22, 2016 at 7:38
  • If you set read-quoted-char-radix to 16 (its default value is 8), entering characters by hexadecimal value becomes a bit easier: C-q 211a RET. Feb 22, 2016 at 17:05

1 Answer 1


The character set used is in the ISO 10646 encoding, which includes the following double stroked letters


and no others. Unfortunately the TeX input method only defines shortcuts for


as describe-input-encoding will tell you. However, How can I add characters to an input method? shows you how to add extra sequences to this input encoding. Thus all you need to know is that double stroked Q is at code point 211A to add this character. To find the code points for other characters have a look at the ISO 10646 standard at http://standards.iso.org/ittf/PubliclyAvailableStandards/index.html .

  • Hmm, I also find a double struck ℍ (for the quaternions), but alas, no double struck O for the octonions. However, there are also two double struck Greek letters: ℾℿ. I have no idea why these are considered so special. The quaternions really are useful, though. The octonions are a bit more marginal. Feb 22, 2016 at 16:57
  • @HaraldHanche-Olsen Yes, I missed H, thank you for pointing that out. The double struck greek letters are indeed strange.... Feb 23, 2016 at 7:28
  • Please report the lack of C Q ... via M-x report-emacs-bug.
    – Stefan
    Feb 23, 2016 at 14:37

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