Before revision:  A wide variety of equivariant layers has been proposed for signals on 2D and 3D Euclidean space , graphs, and the sphere , and it has become difficult to see how all of these methods are related, and how they may be generalized.
After revision:  A wide variety of equivariant layers has been proposed for signals on 2D and the sphere , and it has become difficult to see how all of these methods are related, and how they may be generalized.