In the second part of this thesis we prove that if the Hopf Galois extension is cocentral, and the invariants is a Hopf algebra then $A$ is itself a Hopf algebra.

• 设%24H%24是域%24k%24上的余半单Hopf代数，%24A%24为双代数且%24H%24在%24A%24上有余作用，在论文的第二部分我们证明了 当%24A%24是其余不变量的Galois余中心扩张时，%24A%24上有Hopf代数结构当且仅当它的余不变量子双代数是 Hopf代数。