Struct/The group with two elements.

=Definition=

There is a unique group, up to isomorphism, with two elements. One example is the group $(\ZZ / 2 \ZZ, +)$ of residues, mod $2$, displayed below.

=Properties=


 * The group $\ZZ / 2 \ZZ$ is an exemplifies::Def/Abelian group.
 * It is a cyclic group, generated by $\bar 1$.

=Uniqueness=

There is a unique group with $2$ elements, up to isomorphism.