[texhax] Fwd: kerTeX: TeX and al. under BSD license

Barbara Beeton bnb at ams.org
Tue Dec 20 15:12:11 CET 2011

hello, thierry,

i'd like to comment on just one point ...

    4) What is a right to left line? A left to right line seen from behind
    or in a mirror. What is a top to bottom line? A left to right line
    rotated, with perhaps font metrics having glyphes metrics rotated.
    So is TeX limited to left to right? No, since, with perhaps the
    exception of Frege's ideography, the human normal languages are oriented
    linear, sequential, and there is one previous character and one next.
    So placing whatsits in the DVI file instructing a dvi driver to
    mirror/rotate boxes could do the trick.

not quite.  in arabic, text is written
right-to-left, but numerals (such as years)
are written right-to-left within that context.
so a simple mirror won't work.  and entering
the digits of a year in reverse order won't
gain acceptance by a literate arabic writer.

    So I'm deeply convinced that there are solutions that will keep TeX
    conform to plain TeX usage, but allow more extended schemes.

you might find the article "mixing right-to-left
texts with left-to-right texts" by don knuth and
pierre mackay of interest:
while i've since learned that much of math in
arabic instructional texts is also right-to-left
(with features like "mirrored" radical signs),
the example using a short math string within
right-to-left text is close to what's required.
						-- bb

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