Re: Characters in early sets

Date: Fri Nov 17 2000 - 05:06:11 EST

On Fri, 17 Nov 2000, Doug Ewell wrote:

> Some early character sets have a Greek capital delta. The "obvious"
> mapping is to U+0394 GREEK CAPITAL LETTER DELTA, but there is also
> U+2206 INCREMENT, which shares the identical glyph. - -
> I am inclined to map the delta-as-symbol to U+2206 rather than U+0394.

Incidentally, U+2206 INCREMENT is the character which I chose as an
example in my small "Guide to the Unicode 3.0 standard",
where I discuss the question "how do I find out what the standard really
says about that-and-that character?". My conclusion is that when a
delta-like character is used as a mathematical operator, such as the
Laplacian or difference operator, and not as a letter, it should be
treated as U+2206 in Unicode. However, if you're using, say, capital
alpha, beta, gamma, delta, ... as symbols of quantities just as
A, B, C, ... can be used, then the characters should probably be regarded
as Greek letters.

The characters U+0394 and U+2206 are independent of each other, though
of course they share the same historic origin. The glyphs might be
identical (as they indeed appear to be in the Unicode standard), or
they might be different.

Generally, as regards to Greek letters and symbols resembling them,
there are three ways in which they are handled in Unicode:
1) no distinction is made between a letter, like the small Greek letter pi
  and the well-known mathematical pi symbol; it is still possible that
  a glyph distinction is made in visual presentation, but that would need
  to be based on "higher-level protocols", such as some markup or
  a style sheet (and this does not differ from the possibility of making
  that for any characters)
2) the symbol appears as a separate character, but only as a compatibility
  character, such as the ohm sign (which is compatibility equivalent to
  capital Greek letter omega); the glyphs may be identical or different
3) the symbol appears as a separate character which is not related to a
  Greek letter; for example, the n-ary product character and the capital
  Greek letter pi are "unrelated" in Unicode (i.e. there is no defined
  relationship between the two, though of course it's not the intent to
  deny the historical relationship, or to prohibit the possibility of
  using the same glyph for both).


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