A Bourgain-like property of Banach spaces with no copies of $c_0$
  We give a characterization of the existence of copies of $c_{0}$ in Banach spaces in terms of indexes. As an application, we deduce new proofs of James Distortion theorem and Bessaga-Pe{\l}czynski theorem about weakly unconditionally Cauchy series. 
A. P\'erez and M. Raja
math.FA