Xl. Jiang et Yh. Xu, On the isomorphic classes of Hopf-Galois extensions with normal bases overa commutative ring, ACTA MATH S, 15(4), 1999, pp. 515-524
In this paper we consider the isomorphic classes of H-Galois extensions wit
h the normal basis property over a fixed commutative ring B for a finite Ho
pf algebra H. The result is that when H is cocommutative, then the above is
omorphic classes and the 2-nd cohomology group H-2 (L*, U) are isomorphic a
s groups under the product defined in this paper, where L = B circle times
H, L* = Hom(B) (L, B).