Hopf Galois (Co)Extensions In Noncommutative Geometry
  We introduce an alternative proof, with the use of tools and notions for Hopf algebras, to show that Hopf Galois coextensions of coalgebras are the sources of stable anti Yetter-Drinfeld modules. Furthermore we show that two natural cohomology theories related to a Hopf Galois coextension are isomorphic. 
Mohammad Hassanzadeh
math.KT