The electronic gas in the cuprate superconductors is believed to be
a strongly correlated

quantum system. To carry out an accurate calculation of models
of these systems on large

size lattices is a very challenging problem. Thus, the process of figuring
out which of

these models captures correctly the properties of these materials is
very slow.

Exact diagonalization techniques face an exponentially growing size
of the

Hilbert space with system size. This prohibits a convincing approach
to the

thermodyncamic limit. The main bottleneck with stochastic techniques
is that

we are dealing with fermions where the probability applitudes for

any given configuration does not have a well defined sign and thus

cannot be interpreted as probability distributions.

We have developed Monte Carlo techniques to study such systems.

These techniques are similar in spirit to the so-called Green's function

Monte Carlo method for fermions.

Using these techiques, we find that the effects of the strong short
range correlation

bring the electonic system near an electronic phase separation instability
which

is prevented by the long-range part of the Coulomb interaction.

The presense of this long-range interaction as well as the electron
coupling to the

lattice seem to favor formation of stripes. We believe that the experimenally

seen stripes are a manifestation of the tendency of the system for

phase separation which is compromised in the formation of stripes.

There is a series of papers, including comments and replies which

clarify our beliefs.