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authorNorbert Preining <norbert@preining.info>2019-09-02 13:46:59 +0900
committerNorbert Preining <norbert@preining.info>2019-09-02 13:46:59 +0900
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+[Posted to info-tex on 25 Oct 91; see answer.001]
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+"*** Exercise 3 (fast):
+"What's the most important difference between \- and
+"\discretionary{-}{}{}?
+
+The most important difference between \- and \discretionary{-}{}{} is
+that the latter always puts in the character from font position 45
+("2D, '55) of the current font when a word must be broken at the end of
+a line; \- puts in the character from font position \hyphenchar of the
+current font, which is NOT NECESSARILY position 45. It would be rather
+unusual for \hyphenchar to be something other than 45; in certain
+special applications, however (possibly in some foreign languages as
+well?) a variant value of \hyphenchar can be useful. I have an idea for
+using this in a future exercise . . .
+
+Credit to Donald Arseneau for a correct answer. Thanks to Peter
+Schmitt for providing the perfect opening for another point
+I wanted to make:
+
+> The TeXbook states explicitly:
+> \- is equivalent to \discretionary{-}{}{}
+> and both are internal.
+> I do not see where to the question aims:
+> - control symbol : control sequence
+> - no paramaters : three parameters
+> - two characters : 21 characters to type
+> ???
+
+Schmitt is quoting from the last page of Chapter 25; the point is,
+that in newer versions of the TeXbook that sentence has been revised.
+I'm not sure what the latest printing says, since I don't have a copy,
+but I think it simply refers the reader to Appendix H, where the
+significance of \hyphenchar is explained. \hyphenchar is a feature that
+was added late in the development of TeX82 (TeX82.bug reveals that is
+was not added until May 25, 1983). Even if the source files for the
+TeXbook were immediately updated by Knuth at that time, the changes did
+not appear in the published version being sold to the general public
+until some time later when the first revised edition was published,
+which was no earlier than October 1984, the date of the TeXbook copy
+that I have on hand, and probably later.
+
+The statement of purpose in `Around the bend' #1 said something
+about finding the `best solution', but conspicuously failed to define
+what `best' should mean in this context. It was my intention to address
+this question in future exercises; for now, let me just say that I
+don't intend to arbitrarily rule out of consideration answers such as
+Schmitt's `two characters : 21 characters to type', since depending on
+how you look at it, it could be argued that this is much more
+significant than dumb old \hyphenchar minutiae. I promised that these
+exercises would be challenging; that means, among other things, that
+they won't always be well-defined, well-bounded, or well-behaved, and
+part of the job of finding the `best solution' will be to decide what
+parts of the problem need to be specified further, and to examine the
+ramifications of alternatives.