2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/94557The inhomogeneity of the media or the external forces usually destroy the integrability of a system. We propose a systematic construction of a class of quantum models, which retains their exact integrability inspite of their explicit inhomogeneity. Such models include variable mass sine-Gordon model, cylindrical NLS, spin chains with impurity, inhomogeneous Toda chain, the Ablowitz-Ladik model etc.Latex, 6 pages, no figure; to be published in J. Nonlinear Math. Phys. as Proc. NEEDS'99 (Crete, Greece, June, 1999)Exactly Solvable and Integrable Systemstext