Depth Two Hopf Subalgebras of Semisimple Hopf algebras
  Let H be a finite dimensional semisimple Hopf algebra over an algebraically closed field of characteristic zero. In this note we give a short proof of the fact that a Hopf subalgebra of H is a depth two subalgebra if and only if it is normal Hopf subalgebra. 
Sebastian Burciu