Let B be a Hirata separable and Galois extension of B
G with Galois group
G of order n invertible in B for some integer n, C the center of B, and V
B(B
G) the
commutator subring of B
G in B. It is shown that there exist subgroups K and N of
G such that K is a normal subgroup of N and one of the following three cases holds:
(i) V
B(B
K) is a central Galois algebra over C with Galois group K, (ii) V
B(B
K) is separable C-algebra with an automorphism group induced by and isomorphic with K,
and (iii) BK is a central algebra over V
B(B
K) and a Hirata separable Galois extension
of B
N with Galois group N/K. More characterizations for a central Galois algebra
VB(B
K) are given.
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