@clacke@microca.st exactly, but I wish it were obvious rather than interesting. I chalk up the interestingness to copyright being mindrot. I hadn't thought of contra/covariance analogy before though. I guess you could think of a permissively licensed project as a contravariant function, taking in only permissively licensed material, and emitting material under any/no license, copyleft project as covariant function, taking in any freely licensed material, emitting only copylefted material. (Leaving compatibility for particular licenses to the side.)