The "core" of TeX (actually the only thing that should be called "TeX", the part that Knuth developed and maintains) is so by design decision (his initial decis

The "core" of TeX (actually the only thing that should be called "TeX", the part that Knuth developed and maintains) is so by design decision (his initial decision, that I quoted). What's today used by the other as "TeX" is actually some independently maintained collection around of that core (a "distribution" like TeX Live or MikTeX) and it can and is intentionally "adapted" to the more modern times by its maintainers. http://tex.stackexchange.com/questions/167470/how-to-follow-the-knuth-license http://tex.stackexchange.com/questions/167470/how-to-follow-... Knuth's paraphrased license: "it can be used freely, modified to suit one's needs, but -- if changed -- given a new name." ... "the reason for the name change request/requirement is practical -- to avoid the confusion" Then, once Knuth decided his TeX is stable enough, he even introduced the version numbering system that would make quite obvious his decision that the changes should happen almost never (the version number length increases with every change, making it always harder for everybody to refer to the newer version if it happens): "Since version 3 (released 1989) TeX has used an idiosyncratic version numbering system, where updates have been indicated by adding an extra digit at the end of the decimal, so that the version number asymptotically approaches π. This is a reflection of the fact that TeX is now very stable, and only minor updates are anticipated. The current version of TeX is 3.14159265; it was last updated 2014-01-12." An answer on the StackOverflow discussing the possibility of TeX successor, from 2008: http://stackoverflow.com/questions/303877/is-a-successor-for-tex-latex-in-sight http://stackoverflow.com/questions/303877/is-a-successor-for...