[Tugindia] black board fonts

Kapil Hari Paranjape kapil at imsc.res.in
Tue Aug 19 18:24:53 CEST 2003


Ms. Joshi wrote:
> I have one question about black board fonts which we use using \mathbb 
> command. suppose C, the 'C' printed using mathbb is like writing double 
> 'C' but in actual practise when we actual write the 'C' or letter 
> denoting set of Complex numbers we write it as CI where I very close to 
> 'C' or by C\!\!I gives some what that effect. What is the exact 
> convention for Symbol denoting set of Natural number, Complex numbers?

Not perhaps a TeX question at all...on the other hand TeX *is* about
mathematical typographic questions so here goes ...

The name black-board bold should give it away.

When people got tired of putting little squiggly arrows on top of things
to denote vectors, and tired of saying "this C stands for the field complex
numbers and not the constant C which appears elsewhere'', the natural
choice was to look at typographic convention. Now, in print it was
easy---you used bold-face C or italic C or (horrors) gothic C.
But this was not easy to duplicate on the black-board (except gothic C
which was confusing since some people thought it was G and others
thought that the lecturer's hand had slipped!). So it was natural for
people to adopt "black-board bold" which was to indicate a bold
character by doubling the first vertically oriented stroke in the letter.

This led to the convention, and people got so used to it that it has
come back into the typographic world as a new symbol in addition to the
bold face symbol. This has extended to the point where (at least in
algebraic geometry) the bold-face P and the black-board bold P are used
for different but related objects!

So AMS got someone to create these black-board fonts which mathematicians
demanded in order to duplicate on paper what was a black-board
approximation to usual typographical bold-face!

Hope this clarifies things somewhat.



  It isn't an optical illusion. It just looks like one.

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