Using the methods of regularized moving frames
of Fels and Olver we obtained in our ISSAC'08 paper generating sets of
invariants for the second- and third-orders bivariate hyperbolic and
non-hyperbolic LPDOs. Now we generalize the method to the case of
arbitrary order (hyperbolic and non-hyperbolic) LPDOs. A special choice
of the normalization equations was invented, so that we were able prove
some invariants form a finite (small) generating set of invariants.