Theorem (Cyclic group)
A cyclic group is a group which is equal to one of its cylic subgroups i.e. s.t. where is called the generator of .
Definition (Cyclic subgroup)
For a group , any element one can form a subgroup of all its integer powers called the cyclic subgroup generated by g.
Cor
The only finite subgroups of are the groups consisting of the -th roots of unity with .
Cor
If is a finite field, then is cyclic.