LaTeX Project Public License
The LaTeX Project Public License (LPPL) does not contain all the terms of the LaTeX distribution. According to what can be read, it is a free software license, but incompatible with the GPL because it has many requirements that are not in it.
The file names clause
This license contains complex restrictions on publishing a modified version, including a requirement that any modified file must be renamed.
For LaTeX this requirement is acceptable since it has a functionality that allows matching the names of two files, for example, using the bar file when requesting the foo file. With this functionality the requirement is simply annoying, without it it would be a serious obstacle and we would conclude that it would make the program non-free.
The LPPL says that some files, in certain versions of LaTeX, may have additional restrictions that could make them not free. For this reason, great care would be needed to produce a version of LaTeX that is free software.
Software distribution
The LPPL makes the curious statement that the simple fact of having files on a machine to which a certain number of people have access, in itself constitutes a distribution of the software.
- Note: These comments are made on LPPL version 1.2 (3 September 1999).
License versions
The LPPL license went through the following versions:
- LPPL Version 1.0 March 1, 1999
- LPPL Version 1.1 July 10, 1999
- LPPL Version 1.2 September 3, 1999
- LPPL Version 1.3 December 1, 2003
- LPPL Version 1.3a October 1, 2004.
- LPPL Version 1.3b January 7, 2006.
- LPPL Version 1.3c May 20, 2006. This version is currently (August 2006) the latest.