GNU’s not UNIX. But it can provide a functional equivalent to UNIX. A functional equivalent is something that you could swap the original for and it would perform the same. So a UNIX program, properly recompiled, should run on GNU the same as it would run on UNIX.
Computer programs run by linking to libraries of pre-written code that allow the program to draw on the screen or access the internet or whatever. This linking is a form of reference to existing work, but it is also a form of inclusion, since the program includes the functions of the library. In American law this makes the program a derivative work of the library, a fact that is used by the GNU GPL to enforce copyleft. The program may configure or alter the behaviour of the included library (through the use of callbacks or parameter blocks for example), which would amount to a form remixing (with normal inclusion as sampling).
Can there be a functional equivalent for a cultural work in the same way there can be for a work of computer code? That is, can we produce Free equivalents to canonical works of Proprietary culture? Computer code is essentially mathematics, and there may be more than one way to model the same mathematical algorithm in code. Cultural work may or may not be mathematics, but there is a factor that works against functional equivalency for cultural work. That is authenticity, or the spectre of the fake.
An attempt at a functional equivalent for a cultural work that resembles the original directly will be a fake. Nelson Goodman argues that a work’s status as a fake may have aesthetic import, and that even if a work is not visible as a fake today it may be visible as a fake in the future. It is the aesthetics of a cultural work that are its function, however one conceives of aesthetics. A fake cannot be a functional equivalent, since its status as a fake may be perceptible and this will cause its aesthetic function to fail.
Art has a longer history than code. Prior to the turn of the twentieth century, most of the history or art is available to refer to. With the rise of “no photography” museums and the threat of DRM, this cannot be taken for granted. Most twentieth century art, and all contemporary art, is available only under limited and shrinking Fair Use or Fair Dealing provisions. This is in contrast to the wholesale incorporation of existing iconography and compositions in historical works.
Prior to Modernism, functional equivalents are not currently necessary. For Modernism, because of Goodman, functional equivalents may not be possible. But much modernism is based on abstraction, particularly geometric abstraction. It is based, in other words, on mathematics. So functional equivalents might be possible. Works that directly resemble canonical Modernist works might still infringe copyright. I do not know how different a work would have to be, and if it is too different it would not be a functional equivalent. This leaves work that attempts to achieve indirect functional equivalency, using different colours or shapes or schemata to achieve the same aesthetic or conceptual effects. Where this is not nonsensical, it will be difficult to evaluate equivalency and works may simply not be recognisable as an aesthetic equivalent to a specific work or oeuvre. It will be an original work, and any reference to it will not be the equivalent of a reference to the work it is intended to replace.
Functional equivalency may not work as a foundation for Free Culture as it does for Free Software. We may have to simply ignore modern and contemporary work that cannot be licensed. This fact may still provide a negative creative space for Free Culture to create its forms around. Finding allusive means of reference, locating works that can actually be sampled, and making attempts at indirect functional equivalents may be interesting aesthetic tasks in their own right, may have their own cultural value, and may provide indices as interesting in their own way as the increasingly proprietary recent history of art.