# About the Zassenhaus’s filtration of a group G

The $$n$$-th term of the filtration of Zassenhaus of a group $$G$$, denoted by $$D_n(G)$$, is the subgroup generated by all $$p^k$$-th power of an element $$x\in \gamma_i(G)$$ such that $$ip^k$$ is greater or equal $$n$$. In a text by Zelmanov, i saw that we can get the subgroup $$D_n(G)$$ using the same powers but only of the simple commutators in $$G$$.

Can anyone explain me how to get this or tell me a reference (book or article) that contains the proof of this statement?