Constraints on a quintessence model from gravitational lensing   statistics
  Constraints on an exact quintessence scalar-field model with an exponential potential are derived from gravitational lens statistics. An exponential potential can account for data from both optical quasar surveys and radio selected sources. Based on the Cosmic Lens All-Sky Survey (CLASS) sample, lensing statistics provides, for the pressureless matter density parameter, an estimate of Omega_{M0} = 0.31(-0.14)(+0.12). 
M. Sereno (DSF, Universita` di Napoli, "Federico II", INAF-OAC,   INFN-Sec. Napoli)