A rational approximation to <VV-AA> and its O(p^6) low-energy constant
  Using a sequence of rational approximants and the large-Nc limit of QCD, we estimate the value of the low-energy constant C_87 which appears in the Lagrangian of Chiral Perturbation Theory at O(p^6). 
P. Masjuan and S. Peris (IFAE-Uab)