Contact Integrable Extensions of Symmetry Pseudo-Group and Coverings of   the r-th Modified Dispersionless Kadomtsev -- Petviashvili Equation
  We apply the technique of integrable extensions to the symmetry pseudo-group of the r-th mdKP equation. This gives another look on deriving known coverings and allows us to find new coverings for this equation. 
Oleg I. Morozov