Re: Looking for two mathematical characters

From: Philippe Verdy (
Date: Mon Jun 16 2003 - 19:33:50 EDT

  • Next message: Kenneth Whistler: "Re: Looking for two mathematical characters"

    From: "Kenneth Whistler" <>
    To: <>
    Cc: <>; <>
    Sent: Monday, June 16, 2003 11:53 PM
    Subject: Re: Looking for two mathematical characters

    > Patrick Andries asked:
    > > I'm looking for two mathematical characters.
    > > 2) An angle operator (combining mark ?) looking like this _| , where
    > >
    > > a )
    > > n| a ) n occurrences of a
    > > a ¯ means a )
    > >
    > > n|
    > > obviously a¯ should all be written on a single line.
    > And Philippe Verdy responded (after a long mathematical analysis):
    > > If there such character "_|" in Unicode ? Yes.
    > > With mathematical properties? Yes.
    > > With the correct semantic? No.
    > >
    > > The existing semantic of this mathematical character means "not",

    > To answer Patrick's follow-up question:
    > > Which character are you thinking of ? Which code point ?
    > One would have to surmise that Philippe had U+00AC NOT SIGN in
    > mind, because of what he claimed it meant.

    Sorry, effectively the not operator has effectively the wrong orientation.
    (though there's many variation on the glyph actually used to mean not,
    and such confusion is common).

    Other mathematical operators can also be selected from the technical
    APL operators.

    > which has the "_|" orientation. A usage of the symbol (with a
    > graphic approximation of the intended glyph, parallel to the
    > "_|" ASCII art version) can be seen at:

    Other notations found in ASCII sources is the use of the digraph "^^"
    In fact for plain text notations, any writer would need to define a notation
    explained by full language, and then would use it. If there is really a need
    to specify anexact glyph, MathML or other rich-text or layout language
    will probably offer a better solution.

    Also, because Maths can use any glyph or character as a notation, it is
    not restricted to those characters defined in Mathemetics blocks.
    So the box-drawing characters could produce the desired effect, as
    some examples come with the notation of horizontal division bars:


    (look at this email with a monospaced font preference, on a system supporting
    a font with box drawing characters (as they are used in DOS/OEM charsets)

    Due to this, a plain text mapping (without formatting) could use the
    "┘" character (U+2518) and "─" (U+2500), as in:
      a ┘n
      a ┘(n+1)
    which could be rendered by a 2D layout engine knowing the maths semantics of
    parentheses, and allowing to define custom layout rules in a maths style-sheet:


    Note that box-drawing characters are often much easier to locate in fonts
    than many maths operators.

    However the main problem of these box drowing characters is that they are
    difficult to align on multiple lines as they work best only with coherent
    monospaced fonts, but poorly when multiple monospaced fonts are
    needed (because each font has its own width for the same point size).

    This is not a problem with Unicode, because Unicode plain text normally
    has no layout and end of lines normally mean nothing else than the end of
    a paragraph.

    In the APL subblock of the Misc.Technical block, the character "⌟" (U+231F)
    is also a small bottom-right corner operator, and "⌋" (U+230B) is the second
    (right) character of a floor operator, which can combine with "⌊" (U+230A)
    the first (left) one in the pair. Its representative metrics seems quite good to
    align it with the "n" exponent-order. On Windows, with MS fonts, they are
    supported only with "Arial Unicode MS" (part of Office, not of core Windows
    fonts). May be the Code2000 font has them. The floor characters exist however
    in "Lucida Sans Unicode".

    Floor pairs of characters also exist in non-Unicode fonts like "Symbol", which
    maps the floor pair at 0xEB and 0xFB (with the Symbol encoding, originally
    defined in PostScript). But it seem that they were initially intended to create
    tall square brackets, by joining 2 or more characters vertically.

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