如果一个非平凡的t-设计具有一个旗传递的自同构群,那么t≤6,并且它的自同构群是[(t+1)/2]齐次本原群.因此,一个旗传递5-(v,k,2)设计的自同构群是3-齐次本原置换群.利用3-齐次本原置换群分类定理,讨论了旗传递5-(v,k,2)设计的分类问题.通过分析5-(v,k,2)设计的组合数量关系和3-齐次本原置换群的性质,部分解决了旗传递5-(v,k,2)设计的分类.证明了如果群G是一个非平凡的5-(v,k,2)设计D的旗传递自同构群,那么Soc(G)=PSL(2,q),并且q=2^e或3^e.
If a non-trivial t-design admitting a flag-transitive automorphism group,then t≤6 and its automorphism group is [(t+1)/2] homogeneous.Therefore,the automorphism group of a flag-transitive 5-(v,k,2) design is a 3-homogeneous permutation group.Using the classification theorem of 3-ho-mogeneous permutation groups,the classification of flag-transitive 5-(v,k,2) designs is discussed.By analyzing the combination quantity relation of 5-(v,k,2) design and the characteristics of 3-homogeneous permutation groups,it is proved that if group G is a flag-transitive automorphism group of a nontri-vial 5-(v,k,2)design,then Soc(G)=PSL(2,q),and q=2^e or 3^e.