Re: Solidus variations

7.10.2011 17:07, Hans Aberg wrote:

> There are several solidus (slash) variations.
> What is the intent of those, in as much there been expressed,
> in a mathematical context?

Unicode mostly encodes characters that are in use or have been encoded
in other standards. While not semantically agnostic, it is much less
oriented towards semantic clarifications and distinctions than many
people might hope for (and this includes me, some of the time at least).

> For example, is U+2044 intended for rational numbers,

Yes, and the idea behind it is that programs may format such a number in
a manner typographically suitable for fractions, so that the adjacent
numbers (digit sequences) are affected. This means that e.g. 1⁄2 may
create a rendering similar to some of the glyphs for the character ½.
You probably won’t see this happening in your favorite email program,
text editor, web browser, or even word processor—it’s just the
underlying idea and a possibility, not a requirement (or commonly
implemented).

On the practical side, it may happen that even by virtue of the
different shape of U+2044 (vs. U+002F)—it’s typically in a 45° angle,
though the implementation could be more complicated, even implementing
it as horizonal—, fractions may look somewhat better. But there’s the
risk that U+2044 is not present in the font that will be used (or cannot
be transmitted when using many legacy non-Unicode encodings).

> and U+2215 a long variation of U+002F,

I wouldn’t call it long. Visually, it might be expected to differ from
U+002F by looking specifically like a division operator (as it _is_ a
division operator), as opposite to the semantically ambiguous U+002F. If
it’s longer, I think it’s longer as a consequence of extending from the
baseline to a specific height in a different slope than U+002F.

> which can be used to disambiguate a/b/c/d as in a/b∕c/d = (a/b)/(c/d)?

I don’t quite see what you mean, but if I understand the idea correctly,
it’s not the kind of thing you’re supposed to do. U+2215 is semantically
less ambiguous than U+002F, but the latter too can be used as a division
operator. The choice between U+002F and U+2215 does not affect operator
precedence.

In fact, the relatively new standard on mathematical notations, ISO
80000-2, which identifies the operators by their Unicode numbers,
explicitly says that the symbol “/” used for division is SOLIDUS U+002F.
Maybe they just didn’t think of other possibilities, but in any case
this indicates that U+2215 cannot be expected to the normal, or even
normative, symbol for division.

> And is U+FF0F intended for non-math use?

As the name FULLWIDTH SOLIDUS says, it’s meant for use instead of
SOLIDUS in East Asian writing systems. It’s just a wide variant of
U+002F. So it may have math and non-math use, just as SOLIDUS may.

-- 
Yucca, http://www.cs.tut.fi/~jkorpela/