Discrete Gauge States and$w_\infty$ Charges in c=1 2d Gravity
  We give a general formula for gauge states at the discrete momenta in Liouville theory. These discrete gauge states carry the $w_\infty$ charges. As in the case of the 26D (or 10D) string theory, they are decoupled from the correlation functions and can be considered as the symmetry parameters in the old covariant quantization of the theory. 
Tze-Dan Chung and Jen-Chi Lee