Seminormal subgroup
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In mathematics, in the field of group theory, a subgroup A of a group G is termed seminormal if there is a subgroup B such that AB = G, and for any proper subgroup C of B, AC is a proper subgroup of G.
This definition of seminormal subgroups is due to Xiang Ying Su.
Every normal subgroup is seminormal. For finite groups, every quasinormal subgroup is seminormal.
A good reference for subgroup properties is "A Course in the Theory of Groups" by Derek J.S. Robinson.
