On pointed Hopf algebras associated to unmixed conjugacy classes in S_n
  Let s in S_n be a product of disjoint cycles of the same length, C the conjugacy class of s and rho an irreducible representation of the isotropy group of s. We prove that either the Nichols algebra B(C, rho) is infinite-dimensional, or the braiding of the Yetter-Drinfeld module is negative. 
Nicol'as Andruskiewitsch and Fernando Fantino