and development continues from there. Advanced merging Due to the permanent record of all ancestors and merged revisions, merging can take into account which branch contains which patch, and can do three-way merging based on a shared ancestor revision. Cryptographic signatures Every changeset is stored with a hash to prevent accidental corruption. Using an external file signing program (such as GnuPG or another PGP client), these hashes can also optionally be signed, preventing unauthorized modification if the archive is compromised. Renaming All files and directories can be easily renamed. These are tracked by a unique ID rather than by name, so history is preserved, and patches to files are properly merged even if filenames differ across branches. Metadata tracking The permissions of all files are tracked. Symbolic links are supported and are tracked the same way as files and directories. History and maintainership GNU arch version 1 and tla The original author and maintainer of GNU arch was Thomas Lord who started the project in 2001. The command used to manipulate GNU arch repositories is tla, an initialism for Tom Lord's Arch. Lord started GNU arch as a collection of shell scripts to provide an alternative to CVS. In 2003, arch became part of the GNU project. The GNU arch project forked several times, resulting in both Canonical Ltd.'s now abandoned Baz fork and Walter Landry's ArX project. Both forks provoked a hostile reaction: the ArX fork was due to a serious dispute in direction and Lord was strongly critical of Canonical's approach to announcing the Baz project. In August 2005 Lord announced that he was resigning as the maintainer of GNU arch and recommended that Baz become the main GNU arch project. However, this did not happen: the Baz fork was abandoned by Canonical in favour of the separate Bazaar project, with the 1.5 release of Baz being scrapped in 2006. In October, 2005, Andy Tai announced that Lord and the Free Software Foundation had accepted his offer to be the maintainer of GNU arch. Tai subsequently merged many features from Baz back into tla, but in March 2008 indicated that tla was no longer under active development and was no longer competitive with other version control systems. revc revc was a prototype revision control project by Thomas Lord that he intended to become GNU arch 2.0, designed to be a radical departure from tla and to draw many