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**To**:*math-font-discuss@cogs.susx.ac.uk***Subject**:**Re: More questions on low slots****From**:*Michael John Downes <mjd@MATH.AMS.ORG>***Date**: Tue, 21 Oct 1997 11:07:30 -0400- Sender: mjd@epsilon.ams.org

Frank Mittelbach wrote: > >truetype comes to my mind when we speak about restrictions below 32 > .. > >now you might think this is of no interest since we are doing TeX, but > >this is not true as the commercial vendors are more likely to go with > >such a setup of they can offer those fonts also for other software. To which Hans Aberg replied: > If such restrictions apply, could one not have that in mind, making one > set of dumb fonts which no char's below 32 for dumb software, and having a > set of smart virtual fonts derived from these for the a little smarter TeX? This proposal sounds right to me. For simple math symbols the natural interface, if we ignore the limitations of existing software, is to have a single font including *all* the "commonly used" symbols (including Greek, Latin, slanted, upright, calligraphic, Fraktur, Hebrew, blackboard bold letters; but not other weights like bold and ultra-bold) and call them with something like \mathchar CXXXX where C is the math atom type and XXXX is a four-hex-digit position within the One True Math Font Encoding. (Theoretically speaking more than four hex digits could be advocated, but I think we could limp along with a set of 65536 math symbols for a while.) (This is not Unicode! This is a glyph encoding, not a character encoding.) Delimiters could be done more simply if the base size and the larger sizes were always in the same font: there would be no need then to specify two different character positions in the delimiter code, TeX could just follow next-larger links. The current math font proposal, of course, is intended to work with TeX 3.x which means that it cannot ignore the TeX restrictions of 16 math \fam's and 256 characters per font (total 4096 symbols). As I see it, the current proposal is essentially an interface \mathchar CXXX with some care needed for kerning and next-larger constraints because TeX partitions the 4096 symbols into 16 parts and doesn't do kerning between symbols from different parts. It would seem rather a mistake, however, to reduce further from 256 to 223 per math fam *at the TeX end* of the interface, when TeX only needs to deal with a .tfm file and virtual font mechanisms are readily available. I don't know if this is really what Matthias and Ulrik were speaking of, probably I didn't completely understand. Pragmatically speaking it may be necessary for the moment to have .pfb files that leave slots 0-31 open, and put a hard space in slot 32, but in the discussion of \skewchar etc this issue seems in danger of being being mixed up with the TeX interface issue: I think it would be silly for TeX to see in the .tfm file for a math symbol font that there is a space in slot 32 when it is never going to be used as a math symbol; and in the absence of other criteria the natural place for a skewchar would seem to be position 0 or 255 (which is why I suggested 0 in the first place). Also I think Knuth's use of math mode for the letters of \sin and other operator names is unfortunate. If the letters are to be combined into word-like fragments they should be set in `word mode', i.e., text mode. This becomes more apparent when you try to write a hyphenated operator name such as ess-sup and you find the hyphen turning into a minus sign. Practically speaking the main reason that forced Knuth to set operator names in math mode was no doubt to have them change size automatically in subscripts. But it would not be such a hard task for TeX to do them in text mode as well, if only TeX had a `current math style' variable that could be used to determine the necessary font size at a given point (... that it does not have such a variable is due to the choice of syntax for the generalized fraction commands {...\over...}, as may be known well enough already). In a symbol font where the symbols are only used individually (not combined in operator names) the space character becomes more obviously out of place than before. However, let me hastily contradict myself and say that it might be rather useful in a math symbol font to have a phantom 0 and phantom minus sign character, for tables of numbers. And one of those could naturally go into slot 32 :-) Maybe those are in the proposal already, in fact---I don't recall offhand. Michael Downes, mjd@ams.org

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