A group \((G,\ast)\) is called cyclic group, if there exists an element \(g\in G\) with \(G=\{g^n|~n\in\mathbb Z\}\), i.e. all elements of \(G\) can be represented by positive powers of an element \(g\). In this case, we write \(G=\langle g \rangle,\) i.e. \(G\) is generated by by the element \(g\in G\).
The order of an element $a\in G$ is the smallest natural number $n\in\mathbb N,$ for which $a^n=e$ where $e\in G$ is the neutral element of the group. It is denoted by $\operatorname{ord}(a):=n.$ If such a natural number $n$ does not exist, we write $\operatorname{ord}(a)=\infty.$
Examples: 1
Explanations: 2
Lemmas: 3 4
Proofs: 5 6 7 8 9 10 11 12
Propositions: 13 14 15
Theorems: 16 17