# Re: Solidus variations

From: Hans Aberg <haberg-1_at_telia.com>
Date: Fri, 7 Oct 2011 20:27:07 +0200

On 7 Oct 2011, at 18:58, Murray Sargent wrote:

> One set of examples of the use of these solidus variations occurs in the mathematics linear format described in Unicode Technical Note #28 (http://www.unicode.org/notes/tn28/UTN28-PlainTextMath-v3.pdf). The ASCII solidus (U+002F) described in Section 2.1 is used to represent normal stacked fractions. So a/b automatically builds up to a "over" b separated by a horizontal fraction bar. The fraction slash (U+2044) is used to input skewed fractions as described later in Section 2.1 along with the division slash (U+2215), which is used to enter large linear fractions. In this approach, the full-width solidus (U+FF0F) is treated as an alias for the ASCII solidus to expedite equation entry with East-Asian IMEs.

I recall looked at it before. It does not seem telling to treat expressions like a/b/c/d and 1/2/3/4. The standard way these days in computer languages (or the ones I know), is to parse as division operator, binding to the left. It makes it unusable as a fraction symbol or to display ratios, which would parse as (1/2)/(3/4).

I was playing around with this in a small parser, which is how the question came up. SO I think the ASCII "/" must be used as a division operator.

> U+2215 is a mathematical operator, but the other three appear outside "math zones" in ordinary text. U+FF0F is used in contexts where other full-width Latin letters are present, e.g., in vertical East-Asian layouts. The fraction slash is used to display arbitrary skewed fractions such as ½ when they aren't encoded in Unicode. This is a mathematical context, albeit a simple one.

Then one can use ⁄ U+2044 FRACTION SLASH as a fraction slash. Theres are different rendering, like in TeX $1\over 2$, or ${}^1⁄_2$, the latter which looks nice in XeTeX using XITS. Then ∕ U+2215 DIVISION SLASH can be used as a large division sign, as you also suggest in your paper.

> The ASCII solidus is used in various nonmathematical contexts (dates, alternatives) and reminds one of the ASCII hyphen-minus (U+002D) which also has multiple uses. Unicode has other "slashes" such as the U+27CB RISING DIAGONAL. I have a UTC action item to update Unicode Technical Report #25 with some discussion about U+27CB, so I'll generalize Section 2.15 "Fraction Slash" of that report to compare the usages of the various solidi.

The context I have in mind is a computer that largely sticks to the ASCII tradition, but otherwise uses new Unicode additions to make input more math-like.

Hans
Received on Fri Oct 07 2011 - 13:32:16 CDT

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