设H为有限群G的一个子群。若对任意的素数p‖G|,只要(p·|H|)=1.就有PH=HP,其中P∈Syl_p(G),则H称为在G中是s-半正规的;若存在G的一个主群列1=G_0
A subgroup H of a finite group G is called seminormal in G if it permuts with every Sylow p-subgroup of G with(p,|H|)=1;a subgroup H of a finite group G is said to have the semi-coveravoidance property in G if there is a chief series 1=G_0