Darboux Coverings and Rational Reductions of the KP Hierarchy
  We use the method of Darboux coverings to discuss the invariant submanifolds of the KP equations, presented as conservation laws in the space of monic Laurent series in the spectral parameter (the space of the Hamiltonian densities). We identify a special class of these submanifolds with the rational invariant submanifolds entering matrix models of $2D$--gravity, recently characterized by Dickey and Krichever. Four examples of the general procedure are provided. 
Paolo Casati (Dip. di Matematica, Univ. di Milano, Italy), Gregorio   Falqui (SISSA/ISAS, Trieste, Italy), Franco Magri (Dip...