Injective Hopf bimodules, cohomologies of infinite dimensional Hopf   algebras and graded-commutativity of the Yoneda product
  We prove that the category of Hopf bimodules over any Hopf algebra has enough injectives, which enables us to extend some results on the unification of Hopf bimodule cohomologies of [T1,T2] to the infinite dimensional case. We also prove that the cup-product defined on these cohomologies is graded-commutative. 
Rachel Taillefer