A new infinite set of commuting additional (''ghost'') symmetries is p
roposed for the KP-type integrable hierarchy. These symmetries allow f
or a Lax representation in which they are realized as standard isospec
tral flows. This gives rise to a new double-KP hierarchy embedding ''g
host'' and original KP-type Lax hierarchies connected to each other vi
a a ''duality'' mapping exchanging the isospectral and ''ghost'' ''tim
es''. A new representation of the 2D Toda lattice hierarchy as a speci
al Darboux-Backlund orbit of the double-KP hierarchy is found and para
metrized entirely in terms of (adjoint) eigenfunctions of the original
KP subsystem. (C) 1998 Published by Elsevier Science B.V.