On 7 Oct 2011, at 19:39, Jukka K. Korpela 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).
I am aware of that, but by tracing the origin, one can get hints of usage. >> 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). I am playing around with a small parser on top GMP, so input semantics is the main issue for me. Then I realized that if I let the lexer parse rational numbers, then 1/2/3/4 will parse as (1/2)/(3/4), and not as ((1/2)/3)/4 as expected in ASCII computer programs. But using ⁄ U+2044 FRACTION SLASH as in 1⁄2/3⁄4 = (1/2)/(3/4) becomes unambiguous with 1/2/3/4 = ((1/2)/3)/4. >> 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. If it is not longer, then it unusable as a divisio operator with lower precedence that the ASCII "/". >> 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. One can use the characters how one pleases, but it would not be consistent with its past history. Which is what I suspected and wanted to know. Thanks. Hans
