[OS X TeX] blackboard bold semicolon

[Martin Costabel]

Art Werschulz wrote:
> Hi.
> 
> On Jul 24, 2008, at 4:25 AM, Ross Moore wrote:
> 
>> Hi Art,
>>
>> On 24/07/2008, at 2:17 AM, Art Werschulz wrote:
>>> Hi.
>>>
>>> I am trying to produce a blackboard bold semicolon.  My test file is 
>>> as follows:
>>>
>>> <testfile>
>>> \documentclass[12pt]{article}
>>> \usepackage{amsfonts}
>>>
>>> \begin{document}
>>> $R{\mathbb{;}}S$ and $R;S$ should look different (the semicolon should
>>> be blackboard bold and normal, respectively).

This seems to be the way \mathbb is defined. It uses the command 
\DeclareMathAlphabet, and according to the latex font documentation,

"Only symbols of type \mathalpha will be affected by math alphabet 
commands: within the argument of a math alphabet command they will 
produce the character in slot <slot> of that math alphabet's font. 
Symbols of other types will always produce the same symbol (within one 
math version)."

The semicolon is of type \mathpunct, so it will not be affected by \mathbb.

You can define your own \bbsemi:

\newcommand\bbsemi{\mathop{\mbox{\textbb;}}}

-- 
Martin