My question is about the shaded area in this image.
Does the symbol $L=\bigcup_{g \in G} T^{g}$ means that $L$ is a union of sets or $L=\langle T^{g}, g\in G \rangle$? If it means the first one, then how did the authors prove that $L$ equals to that union? If it means the second one, then how did the author conclude that all the elements of order p or 4 (if $p=2$) of $L$ are contained in $K$? I like to add that $L/K$ is an abelian p-group of exponent $p$.
My question comes from the the paper BaoJun Li, ZhiRang Zhang: The influence of s-conditionally permutable subgroups on finite groups, Sci. China Ser. A-Math. (2009) 52: 301; DOI: 10.1007/s11425-009-0028-4
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