We can do two things here, we can raise `NotImplemented` error and the other option is, as mentioned in the idea page, is creating and returning an unevaluated Solve object. One advantage of raising NotImplemented error is that it will
explicit tell the user that work on sympy is not yet complete and they might help us
improve it. @asmeurer can you tell me about some particular use cases of unevaluated solve object.