Premise: Octopus: The Best of Syd Barrett, released 29 May 1992, is a one-disc compilation of songs by Syd Barrett. It contains songs from his two solo albums, "The Madcap Laughs" and "Barrett", and the compilation outtakes/rarities album, "Opel". This album was later superseded by "".
Hypothesis:  Syd Barrett had an album that consisted of rare songs, it was called Opel.