Re: symbols/codepoints for necessity and possibility in modal logic

From: Asmus Freytag <>
Date: Fri, 19 Jul 2013 01:53:21 -0700

Unicode cannot be the arbiter of mathematical (or other) notation, but,
within limits, you could ask for some annotations if this would help
ensure that there's some uniformity in how people pick symbols for
certain purposes.

Why not contact the relevant publishers and find out what they are using?


On 7/19/2013 12:43 AM, Stephan Stiller wrote:
>> What is wrong with using DIAMOND OPERATOR?
> "wrong" is strong wording and goes beyond what I suggested or implied,
> but it's not clear to a user of Unicode that it's the right fit
> either. There are a couple of indicators factoring in:
> * The charts mention modal logic in conjunction with ◻ (U+25FB) and
> ⟠ (U+27E0) but not with ⋄ (U+22C4).
> * The glyph in the code charts is tiny (and that of Cambria Math is
> tiny as well). Typographically you see various things (a lozenge,
> fallback to letter-M) in esp older books, but it feels like it's
> meant to be an orthogonal diamond of perhaps slightly less area
> than the box but descending a little above and below the box,
> which is somewhat taller than x-height. The book by {Blackburn, de
> Rijke, Venema} has glyphs that look right. This is more than a
> guess: it makes sense if they have similar visual weight, as they
> are – literally – defined to be duals of one another; but whether
> you can make them geometrically congruent symbols of equal area I
> haven't tested (this might have the diamond ascend too far).
> * The vague notion of "operator" (a word with different meanings in
> math, from /logical relation/ to /[non-logical/non-relational]
> mapping of type A×A→A or perhaps A×A→B/ to /(linear) map (between
> say vector spaces) in linear algebra/) in this context (in the
> code charts) seems to refer to something like my middle meaning,
> which is likely to use a smaller symbol around x-height in
> placement and dimensions.
> * The glyph of ⬦ (U+2B26) seems to have a more appropriate name, but
> in the charts I like ◇ U+25C7. The differently sized square-like
> symbols are hard to semantically tell apart in/from the charts anyway.
> * These symbols are the first two visually distinct ones you define
> in modal logic, so they're well-known and standardized in meaning
> for anyone who had had contact with the field. It's surprising
> they're not explicitly named in the charts. (There's stuff like
> the outdated horseshoe for logical implication popping up in the
> relevant books, but that is a leftover or outdated logic notation
> in general.) So for box and diamond it's quite reasonable to be
> expecting a standard math font to provide them just right out of
> the box; for whatever commonly used box-like symbols in math there
> are, one would assume that there are corresponding codepoints;
> otherwise you'd have to choose a different font.
> Stephan
Received on Fri Jul 19 2013 - 03:56:52 CDT

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