Ciro Santilli @cirosantilli 34

Has $SU(2)$ as a double cover.

Basically it is a larger space such that there exists a surjection from the large space onto the smaller space, while still being compatible with the topology of the small space.

We can characterize the cover by how injective the function is. E.g. if two elements of the large space map to each element of the small space, then we have a double cover and so on.

Double cover of $SO(3)$.

Isomorphic to the quaternions.