On pointed Hopf algebras associated with the symmetric groups
  It is an important open problem whether the dimension of the Nichols algebra B(O,\rho) is finite when O is the class of the transpositions and \rho is the sign representation, with m>= 6. In the present paper, we discard most of the other conjugacy classes showing that very few pairs (O,\rho) might give rise to finite-dimensional Nichols algebras. 
Nicol\'as Andruskiewitsch, Fernando Fantino and Shouchuan Zhang