$\mathbb{Z}_p$, $\mathbb{Q}_p$, and the ring of Witt vectors

No.8:

Recall $\Lambda(A)=1+A[[T]]T$ for a formal variable $T$. To clearly describe the variable, we will denote it as $\Lambda_{(T)}(A)$. It is additively topologically generated by $\{[a]_T=1-aT; a \in A\}$. the set of all Teichmüller lift of the elements $a\in A$.