Anomaly In 2d-Gravity Coupled To Matter Fields
  In 1+1 dimensions, the Wheeler-DeWitt equation cannot be imposed owing to an anomaly in its commutator with the diffeomorphism constraint. A similar obstruction prevents also a semiclassical definition of a WKB local time. (Talk given at the 7th Marcel Grossman Meeting on General Relativity, Stanford, July 28, 1994.) 
Daniel Cangemi