From: Jim Allan (jallan@smrtytrek.com)
Date: Fri May 30 2003 - 10:38:12 EDT
Ken Whistler posted:
> And what I pointed
> out earlier is that, in *linguistic* usage, the slashed zero
> glyph is clearly an acceptable glyphic variant of the
> empty set symbol. So to claim it is "completely unrelated"
> is to manifestly ignore actual practice.
Indeed.
Donald Knuth, a mathematician and author of books on programming,
disgusted with the continued worsening of typography for publication of
mathematical texts, in the 1980's invented the TeX typesetting
programming system and the Metafont font creating system and produced a
number of fonts himself which are still used.
He used the slashed 0 for the empty set symbol in his cmsy10 font for
mathematics.
See http://www.mozilla.org/projects/mathml/fonts/encoding/cmsy-ttf.gif
for the forms of this font. It is encoded as U+2205 at
http://www.mozilla.org/projects/mathml/fonts/encoding/cmsy-ttf-encoding.html.
See also
http://www.usefulcontent.org/docs/manuals/REC-MathML2-20010221/isoamso.html
for some mathml characters and their unicode encodings.
The character "empty" is encoded as U+2205 plus the variation selector
U+FE00 and has the description "/emptyset - zero, slash" and the alias
"emptyset".
The following character "emptyv" is encoded simply as U+2205 and has the
description "/varnothing, circle, slash" and the alias "varnothing".
But the glyph forms of both are given as slashed zero, though that for
"empty" is slightly wider. (I suspect an error in the emptyv glyph shown
here.)
At
http://www.usefulcontent.org/docs/manuals/REC-MathML2-20010221/byalpha.html
the entities empty and emptyset are both assigned to U+2205 followed by
U+FE00 while emptyv is again just U+2205.
That the differing forms are indicated by a variation selector indicates
that the forms are seen to be "primarily glyphic variations" (see
http://www.unicode.org/reports/tr25/#13_7_variation_selectors).
That both "emptyset" and "empty" are applied to the slashed zero while
"emptyv" (I presume meaming "empty variant") is applied to slashed
circle would seem to indicate that to the creators of mathml, as well as
to Donald Knuth, the slashed zero form is felt to be the more normal
glyph for empty set (and for other indications of emptiness, nullity, etc.)
Jim Allan
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