2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/38945The COntractor REnormalization group (CORE) approximation, a new method for solving Hamiltonian lattice systems, is introduced. The approach combines variational and contraction techniques with the real-space renormalization group approach and is systematically improvable. Since it applies to lattice systems of infinite extent, the method is suitable for studying critical phenomena and phase structure; systems with dynamical fermions can also be treated. The method is tested using the 1+1-dimensional Ising model.3 pages, compressed-uuencoded PostScript file, Edinburgh Preprint 94/547, talk presented at ICHEP 94, July 1994, GlasgowHigh Energy Physics - Latticetext