  The COntractor REnormalization group method was devised in 1994 by
Morningstar and Weinstein. It was primarily aimed at extracting the physics of
lattice quantum field theories (like lattice Quantum Chromodynamics). However,
it is a general method of analyzing Hamiltonian lattice systems, e.g. Ising,
Heisenberg or Hubbard models. The aim of this work is to show the application
of CORE to one-dimensional quantum systems -- the Heisenberg zig-zag model and
the Hubbard chain. As a test of the method, the ground state energy of these
systems will be calculated.
