  A representation of the Quantum Toroidal Algebra of type sl(N) is constructed
on every irreducible integrable highest weight module of the Quantum Affine
Algebra of type gl(N). As an intermediate step in the construction, we obtain a
quantum analogue of the classical level-rank duality, describing the reciprocal
decomposition of the q-Fock space with respect to mutually commutative actions
of U_q(gl(N)^) of level L, and U_q(sl(L)^) of level N.
