Boundary Ground Ring and Disc Correlation Functions in Liouville Quantum   Gravity
  We construct the boundary ground ring in c < 1 open string theories with non-zero boundary cosmological constant (FZZT brane), using the Coulomb gas representation. The ring relations yield an over-determined set of functional recurrence equations for the boundary correlation functions, which involve shifts of the target space momenta of the boundary fields as well as the boundary parameters on the different segments of the boundary. 
Ivan K. Kostov