AF ormal Investigation ofDiff3

2 Yahoo Abstract.Thediff3algorithm is widely considered the gold standard formerginguncoordinatedchangestolist-structureddatasuchastextfiles. Surprisingly, its fundamental properties have never been studied in depth. We o!er a simple, abstract presentation of thediff3algorithm and investigate its behavior. Despite abundant anecdotal evidence that peo- ple finddiff3's behavior intuitive and predictable in practice, charac- terizing its good properties turns out to be rather delicate: a number of seemingly natural intuitions are incorrect in general. Our main result is ac areful analysis of the intuition that edits to "well-separated" regions of the same document are guaranteed never to conflict.