Editing TeX (section)

===Licence===
Donald Knuth has indicated several times<ref>{{cite journal |last1=Knuth |first1=Donald E. |date=1986 |title=Remarks to Celebrate the Publication of Computers & Typesetting |url=https://tug.org/TUGboat/tb07-2/tb15knut.pdf |journal=TUGboat |volume=7 |issue=2 |pages=95–98 |access-date=6 December 2024}}</ref><ref>{{cite journal |last1=Knuth |first1=Donald E. |date=1990 |title=The Future of TeX and METAFONT |url=https://www.tug.org/TUGboat/tb11-4/tb30knut.pdf |journal=TUGboat |volume=11 |issue=4 |page=489 |access-date=6 December 2024}}</ref><ref>{{cite web |url=https://www.kyotoprize.org/wp-content/uploads/2019/07/1996_A.pdf |title=Digital Typography: 1996 Kyoto Prize Lecture |last=Knuth |first=Donald Ervin |publisher=The Inamori Foundation |date=November 1, 1997 |website=Kyoto Prize |access-date=December 6, 2024}}</ref><ref name="DigitalTypography">{{cite book | last=Knuth | first=Donald E. | title=Digital Typography | publisher=Center for the Study of Language and Information Publications | publication-place=Stanford, Calif | date=1999 | isbn=978-1-57586-010-7 }}</ref> that the source code of TeX has been placed into the "[[public domain]]", and he strongly encourages modifications or experimentations with this source code. However, since Knuth highly values the reproducibility of the output of all versions of TeX, any changed version must not be called TeX, or anything confusingly similar. To enforce this rule, any implementation of the system must pass a test suite called the TRIP test<ref>{{Citation |url=ftp://tug.ctan.org/pub/tex-archive/systems/knuth/dist/tex/trip.tex |title=CTAN |contribution=Trip |type=source code |format=TeX}}</ref> before being allowed to be called TeX. The question of licence is somewhat confused by the statements included at the beginning of the TeX source code,<ref>{{Citation |first=Donald E |last=Knuth |title=TeX: The Program |series=Computers and Typesetting |volume=B |place=Reading, MA |publisher=Addison-Wesley |year=1986 |isbn=0-201-13437-3 |url-access=registration |url=https://archive.org/details/texprogram00knut}}</ref> which indicate that "all rights are reserved. Copying of this file is authorized only if&nbsp;... you make absolutely no changes to your copy". This restriction should be interpreted as a prohibition to change the source code ''as long as the file is called tex.web''. The copyright note at the beginning of tex.web (and mf.web) was changed in 2021 to explicitly state this. This interpretation is confirmed later in the source code when the TRIP test is mentioned ("If this program is changed, the resulting system should not be called 'TeX{{'"}}).<ref>[https://books.google.com/books?id=PA-Rhb_QSAwC&dq=tex+in+public+domain+knuth&pg=PA227 Open Source: Technology and Policy] by Fadi P. Deek, James A. M. McHugh "Public domain", page 227 (2008)</ref> The [[American Mathematical Society]] tried in the early 1980s to claim a [[trademark]] for TeX. This was rejected because at the time "TEX" (all caps) was registered by [[Honeywell]] for the "Text EXecutive" text processing system.{{Citation needed|date=April 2010}}