[OS X TeX] blackboard bold semicolon

Ross Moore ross at ics.mq.edu.au
Thu Jul 24 09:40:19 EDT 2008

Hi Art,

On 24/07/2008, at 11:34 AM, Art Werschulz wrote:

>>> \begin{document}
>>> $R{\mathbb{;}}S$ and $R;S$ should look different (the semicolon
>>> should
>>> be blackboard bold and normal, respectively).
>>
>> Sorry, I cannot agree with you here.
>> What is a "blackboard bold semi-colon" meant to mean?
>> How is it different to a normal semi-colon?
>> If there is a different meaning, where does this occur
>> within existing literature?
>
> I am using the text
>    Neville Dean, "Essence of Discrete Mathematics"  (Prentice-Hall
> PTR, 1996)
> in a course that I'm teaching.  Unfortunately, this text uses a
> blackboard bold semicolon to represent what you might call
> covariant composition of relations, as opposed to the usual $\circ$
> that's used for the standard (contravariant) notation.

OK; so there is a verifiable precedent.

In that case it is worth advising Barbara Beeton of the
American Mathematical Society, so that it can be considered
for future inclusion in Unicode.

I've Bcc'd her on this message --- she'll probably ask for
some more details, if she's not already familiar with this
character and its usage.

> I'm giving an exam on this material soon; for this particular
> class, it would be a bad idea to change the author's (admittedly
> idiosyncratic) notation.  So I'm more or less forced to use same on
> the exam.  :-(

As for using it, try the following:
(it's a bit clunky, but works!)

\newcommand{\cov}{\mathrel{\hbox{\textbb{;}}}}

$\mathbb{A\cov B}$

If that isn't giving the spacing that you want,
then try:

\newcommand{\cov}{\mathord{\hbox{\textbb{;}}}}

Hopefully you don't need this with super/subscripts.

>
> Art Werschulz
> 207 Stoughton Avenue, Cranford  NJ 07016-2838
> (908) 272-1146

Hope this helps,

Ross

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Ross Moore                                       ross at maths.mq.edu.au
Mathematics Department                           office: E7A-419
Macquarie University                             tel: +61 (0)2 9850 8955
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