# [OS X TeX] blackboard bold semicolon

Art Werschulz agw at comcast.net
Thu Jul 24 06:34:13 EDT 2008

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).
>
> 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.   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.  :-(

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