The NSF (10671082) of China, the 985 Program of Jilin University the Key Laboratory of Symbolic Computation and Knowledge Engineering of Ministry of Education the Postgraduate Students Innovative Fund
A subgroup H of a group G is said to have the sub-cover-avoidance property in G if there is a chief series 1=G0≤G1≤≤Gn=G,such that Gi-1 (H∩Gi)■■G for ever