Connected component of identity

Definition

In a topological group, the connected component of identity is the connected component of the identity element of the group with respect to the underlying topology. The following are true:

1. The connected component of identity is a topological automorphism-invariant subgroup of the whole group, and in particular, it is a normal subgroup of the whole group.
2. The other connected components are all cosets of this subgroup. Since the connected component of identity is a normal subgroup, the left cosets are the same as the right cosets.