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Hello good people of Emacs!

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

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

Any Ideas what can be the source of this error?

Empty_Mind
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    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 http://emacs.stackexchange.com/q/3104/2710 which may help with how to extend the input method. – Andrew Swann Feb 21 '16 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 '16 at 22:54
  • @Drew OK done, but this is very close to being a duplicate. – Andrew Swann Feb 22 '16 at 07:38
  • 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`. – Harald Hanche-Olsen Feb 22 '16 at 17:05

1 Answers1

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

C H N P Q R Z

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

N P R Z

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 .

Community
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Andrew Swann
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  • 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. – Harald Hanche-Olsen Feb 22 '16 at 16:57
  • @HaraldHanche-Olsen Yes, I missed H, thank you for pointing that out. The double struck greek letters are indeed strange.... – Andrew Swann Feb 23 '16 at 07:28
  • Please report the lack of C Q ... via `M-x report-emacs-bug`. – Stefan Feb 23 '16 at 14:37