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Let $G$ be a finite group. The Wielandt subgroup of $G$ is defined to be the intersection of all the normalizers of the subnormal subgroups of $G$ i.e. $$w(G) = \bigcap_{H \triangleleft \triangleleft G} N_G(H)$$ Now we can define the Lower Wielandt Series by the descending normal series given by $w_0(G) = G$, $w_1(G)= w(G)$, $$w_{\alpha +1}(G) = \hspace{-3mm}\bigcap \limits_{K\in \;\Omega_{\alpha}(G)}\hspace{-3mm}w(K)$$ where $\Omega_{\alpha}(G)$ is the set of subgroups of $G$ that contain $w_\alpha(G)$ and $$w_{\lambda}(G) = \bigcap \limits_{\beta < \lambda}w_\beta(K) \;\;\text{ if $\lambda$ is limit ordinal}$$ We denote the last term of this series by $\bar w(G)$

Question: Suppose that we have the subgroup $H\bar w(G)$ for some $H\unlhd G$. Is it true that $\bar w(G) \subset w(H\bar w(G))?$

Now, I know that $\bar w(G)$ is subnormal in $G$ and since $\bar w(G) \leq H\bar w(G)$, $\bar w(G)$ is subnormal in $H\bar w(G)$. I'm not sure how to proceed. Any possible guidance will be appreciated. I have asked this question MSE and nobody responded thus I have posted it on this forumd

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    $\begingroup$ In your MSE post you had $H \le G$, but now you have $H \unlhd G$. With $H \unlhd G$ it's easy because all subnormal subgroups of $H\bar{w}(G)$ are subnormal in $G$. $\endgroup$
    – Derek Holt
    Commented Mar 14, 2017 at 6:34
  • $\begingroup$ What is the question? $\endgroup$ Commented Mar 14, 2017 at 6:56
  • $\begingroup$ @DerekHolt, Yes I erroneously had $H\leq G$. I understand that $H\bar w(G)$ is subnormal in $G$, and thus $w(H\bar w(G)) \leq w(G)$. I still don't see how $\bar w(G) \subset w(H\bar w(G))$ would follow from this $\endgroup$
    – R Maharaj
    Commented Mar 14, 2017 at 7:24
  • $\begingroup$ @AndreasThom, I want to show that $\bar w(G) \subset w(H\bar w(G))$ $\endgroup$
    – R Maharaj
    Commented Mar 14, 2017 at 7:25
  • $\begingroup$ @DerekHolt, Correction. I can see how it follows. Since each subnormal subgroup of $H\bar w(G)$ is subnormal in $G$, we have that $w(G) \leq w(H\bar w(G))$ rather than the other way round. And since $\bar w(G) \leq w(G)$. The proof is complete. $\endgroup$
    – R Maharaj
    Commented Mar 14, 2017 at 7:35

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