Re: @U{xxxx} -- some TeX characters with a capital don't seem to work

[Gavin Smith]

On Tue, Jul 04, 2017 at 10:25:39AM +0200, Benno Schulenberg wrote:
> 
> Op  4-07-2017 om 08:26 schreef Gavin Smith:
> >On Mon, Jul 03, 2017 at 05:31:14PM +0200, Benno Schulenberg wrote:
> >>
> >>\DeclareUnicodeCharacter{25A1}{\ensuremath\Box}%
> >>\DeclareUnicodeCharacter{25C7}{\ensuremath\Diamond}%
> >>\DeclareUnicodeCharacter{2A1D}{\ensuremath\Join}%
> >
> >@Diamond is not defined either, nor is @Join.
> 
> So... what that section of texinfo.tex does is: translate a code
> to a named texinfo character?  But where are these texi characters
> defined?  Because, for example, @U{25B3} works, producing a triangle,
> but I can't find @triangle anywhere in texinfo's code?  Where does
> it come from?
> 

It is built into TeX (or more precisely plain TeX). This file is called 
plain.tex. On my computer, it is located
at /usr/share/texmf/tex/plain/base/plain.tex, but may be elsewhere 
depending on how TeX was installed. It is already preloaded when TeX 
starts running.

Some of these definitions for Unicode characters were copied from a 
LaTeX reference manual. Most of them work with plain TeX but apparently 
a few of them are wrong.

If this page is reliable:

http://www.fileformat.info/info/unicode/char/25c7/index.htm

U+25C7 should be an unfilled diamond (the filled diamond is U+25C6).  
@diamond is probably okay to use for this.

The problem with supporting a filled diamond is that there seems to be 
no glyph in the default set of fonts for TeX that corresponds to that 
symbol. That's about as far as we can go with Unicode support.

> \diamond is already used for U+22C4 and \diamondsuit for U+2662.

The diamond suit glyph is slightly different as it is more elongated in 
a vertical direction whereas the diamond symbol appears to be a square 
resting on one corner. There's probably no harm in using \diamond for 
both U+22C4 and U+25C7.