A non-nilpotent finite group whose proper subgroups are all nilpotent is called a Schmidt group. A subgroup A is said to be seminormal in a group G if there exists a subgroup B such that G = AB and AB 1 is a proper subgroup of G, for every proper subgroup B 1 of B. Groups that contain seminormal Schmidt subgroups of even order are considered. In particular, we prove that a finite group is solvable if all Schmidt {2, 3}-subgroups and all 5-closed {2, 5}-Schmidt subgroups of the group are seminormal; the classification of finite groups is not used in so doing. Examples of groups are furnished which show that no one of the requirements imposed on the groups is unnecessary.We deal with finite groups only. A non-nilpotent group whose proper subgroups are all nilpotent is called a Schmidt group. The Schmidt groups were brought in sight in [1] where it was proved that such are biprimary, and also that in each of these groups, one Sylow subgroup is normal and the other is cyclic. A detailed review of the structure of Schmidt groups and their applications in finite group theory can be found in [2].A subgroup A is said to be seminormal in a group G if there exists a subgroup B such that G = AB and AB 1 is a proper subgroup of G, for every proper subgroup B 1 of B. In this setting, the subgroup B is called a supercomplement to the subgroup A. Obviously, a subgroup of prime index is always seminormal. A quasinormal subgroup (i.e., one that commutes with all subgroups of the group) will be seminormal. In a simple group P SL(2, 5), the subgroup A isomorphic to an alternating group of degree 4 is a seminormal Schmidt subgroup, but A is neither quasinormal nor subnormal.In the present paper, we look at groups that contain seminormal Schmidt subgroups of even order. We will argue for the following two theorems.
THEOREM 1. If A is a seminormal Schmidt subgroup of a group G, and the subgroupTHEOREM 2. If all Schmidt {2, 3}-subgroups of a group G are seminormal, then the group G is 3-solvable.COROLLARY. If all Schmidt {2, 3}-subgroups and all 5-closed Schmidt {2, 5}-subgroups of a group G are seminormal then the group G is solvable.In proving the theorems and the corollary, we will not appeal to the classification of finite simple groups. * Supported by BelFBR grant Nos. F05-341 and F06MS-017.1 Gomel Engineering Institute under the Belarussian Ministry of Extraordinary Situations; knyagina@inbox.ru.