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This is exercise 12.17

(This is a sequel to exercise 12.2, but it's trickier.) Describe the result of \line{\hfil A puzzle.\hfilneg}

This is exercise 12.2

Describe the result of \line{\hfil\hfil What happens now?\hfil} \line{\hfill\hfil and now?\hfil}

The answer to exercise 12.17 reads:

... (In this case, TeX's rule about infinite glue differs from what you would get in the limit if the value of 1 fil were finite but getting larger and larger. The true limiting behavior would stretch the text `A puzzle.' in the same way, but it would also move that text infinitely far away beyond the right edge of the page.)

Example from the question is equivalent to this:

\hbox to\hsize {\hskip 0pt plus 1fil A puzzle.\hskip 0pt plus -1fil}

How in terms of this does one interpret the words "if the value of 1 fil were finite" and "true limiting behavior"?

1 Answer 1

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\hfilneg isn't a minus value but rather a negative plus value:

\hbox to\hsize {\hskip 0pt plus 0pt A puzzle.\hskip 0pt plus -0pt}

\hbox to\hsize {\hskip 0pt plus 10pt B puzzle.\hskip 0pt plus -10pt}

\hbox to\hsize {\hskip 0pt plus 100pt C puzzle.\hskip 0pt plus -100pt}

\hbox to\hsize {\hskip 0pt plus 1000pt D puzzle.\hskip 0pt plus -1000pt}

\hbox to\hsize {\hskip 0pt plus 1fil E puzzle.\hskip 0pt plus -1fil}

\hbox to\hsize {\hfil F puzzle.\hfilneg}

\bye

Note the last two examples E and F are the same, but the point is they do not correspond to the limiting case of A-D as the finite skip gets larger.

enter image description here

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  • Fixed the question. BTW, should "was" be used instead of "were" in the answer? (because the concept of 1fil is regarded here as a singular thing) Commented Aug 26, 2015 at 23:09
  • @IgorLiferenko were is OK here it's not singular/plural but rather the conditional would .. if ... were (but don't ask an Englishman about English grammar:-) Commented Aug 26, 2015 at 23:48
  • why the case B C D show nothing on the final page?
    – yanpengl
    Commented May 12, 2022 at 14:48
  • @Lucas better to ask new questions than comment on old ones, but they are all off the page, to the right like \hbox{\hskip 100cm B \hskip -100cm} Commented May 12, 2022 at 16:35
  • @DavidCarlisle thanks for hint. I now relize that \hskip 0pt plus 10pt a b\hskip 0pt plus -10 pt is very different from \hskip 0pt plus 1fil a b\hskip 0pt plus -1fil. after multiplying the glue set ratio, the left and right glue of the former have a big width.
    – yanpengl
    Commented May 13, 2022 at 2:36

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