Barbara Beeton said (TUGboat vol. 34, pag. 4):

As noted on Don Knuth's TeX web pages, www-cs-faculty.stanford.edu/~knuth/abcde.html, he "intend[s] to check on purported bugs again in the years 2013, 2020, 2028, 2037, etc."

So 2013 is the year for a debugging session.

My question

After DEK has debugged (i.e. changed) TeX, will there be identical changes in pdfTeX, XeTeX, and the other engines according to the changes in TeX?

  • I think what the developers should keep in mind for the future is Where do you draw the line from version 2.0.something.something to a new different thing? Commented May 30, 2013 at 14:24
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    although most of the answers so far are rather frivolous, i think the question whether the post-2013 implementations of the variant engines will remain (backward-)compatible with knuth's tex engine is a legitimate concern. my vote is to not close it, but encourage answers from the implementors responsible for the variant engines. Commented May 30, 2013 at 18:20
  • DEK's write-up of the TeX tune-up may be found online at The TeX tuneup of 2014. (Aside: You may have to be a TeX Users Group (TUG) member in order to access this link before Apr. 2015.)
    – Mico
    Commented May 5, 2014 at 20:21
  • 1
    See also What's new in TeX, version 3.14159265? Commented Aug 6, 2017 at 19:31

3 Answers 3


My dark guesses, freely adapted from Sybill Trelawney's divination lessons:


  • Since the latest changes (3.1415926) were put into the main TeX engines (TeX, pdfTeX, LuaTeX, XeTeX) I would expect the same for changes of this year, because these engines are more or less maintained.


  • Changes are unlikely because of a very dark death.
  • Maintenance of XeTeX has ended.


  • Religious wars about the state of TeX and its creator.
  • Maintenance of pdfTeX has ended.


  • Hardware and software are in the hands of global companies and governments. Free software, compilers, programs are forbidden. Free texts are handwritten and masqueraded as artwork.

2047 etc.

  • What is TeX?
  • 10
    Unfortunately, your "2037" entry is the dream of many large companies, such as Apple. They would love nothing more than to have a lock on everything that runs on the systems they produce, and will start by outlawing individually written software, on the specious grounds of "security". Only approved software written by the hardware manufacturer will be runnable. And it will happen well before 2037, I'm afraid. Hardware is a commodity; software is where the money is. When free software is outlawed, only outlaws will have free software.
    – Phil Perry
    Commented May 30, 2013 at 16:00
  • 4
    I am sure His Noodly Appendages will help us stay free beyond 2037!
    – Xavier
    Commented May 30, 2013 at 16:05
  • So Continuum is true...
    – Nick T
    Commented May 30, 2013 at 21:27
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    Weirdly, it also makes sense if you read backwards !?
    – percusse
    Commented Jun 16, 2013 at 22:37

Yes. For engines that are distributed as change files, this should more or less happen automatically when tex.web is updated (if there are any updates). For other engines this has to be done manually, usually by the indefatigable Peter Breitenlohner for TeXLive.

But don't hope for much; the kind of fixes that Knuth is likely to accept are usually cosmetic or marginal changes that have no effect on the actual typesetting.

  • 3
    My general understanding is that these days he's only willing to fix bugs that cause the system to crash (e.g., segfault) or to behave unpredictably (e.g., race conditions or uninitialized memory access, if such are even possible under the circumstances). His philosophy seems to be that someone could be relying on just about any other sort of bug, either at the document or the tool chain level.
    – dfeuer
    Commented May 30, 2013 at 18:26
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    So basically … xkcd.com/1172 Commented May 31, 2013 at 12:44

The number of changes Knuth might make this year to the core TeX engine code will be, I suspect, somewhere between a handful and vanishingly small. Regardless, any such changes should trivially be incorporated into future builds of pdftex, XeTeX, etc. using the usual automated Web2C/".ch" file compilation processes. There are, of course, a whole slew of large- to very large-scale changes that TeX's code could benefit from, but DEK isn't in that business and he has other more important work to do these days. Plus were I in his shoes, I'd be worried about any changes large enough to create a new pagination of the typeset ("literate") version of the code/book.

Were I betting man, I would wager $1.00 (hex) from the Bank of Sans Serif that at least one minor typo (so to speak) will be fixed in the code's English exposition this year. But I'm not because I don't want to risk losing the check I received for finding it.

  • 2
    Welcome to TeX.SX!
    – mafp
    Commented Jun 16, 2013 at 22:09
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    In fact, looking at a diff of the tex.web files, there was more than one change in the code's English exposition. In one place "in case hanging indentation or \parshape is in use" was changed to "…are in use", and three more modules were added to the index entry for "inner loop". Commented Aug 6, 2017 at 20:03

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