  Analogues of the KP and the Toda lattice hierarchy called dispersionless KP
and Toda hierarchy are studied. Dressing operations in the dispersionless
hierarchies are introduced as a canonical transformation, quantization of which
is dressing operators of the ordinary KP and Toda hierarchy. An alternative
construction of general solutions of the ordinary KP and Toda hierarchy is
given as twistor construction which is quatization of the similar construction
of solutions of dispersionless hierarchies. These results as well as those
obtained in previous papers are presented with proofs and necessary technical
details.
