  It is shown that the Wegner model of disorder contains a system of
constraints which is important whenever the disorder is not weak and which is
responsible for localization in D > 2 dimensions. When the disorder is strong
the constraints divide the phase space into an exponentially large number of
domains; the localized phase is a glass. This work is based on recently
developed field theories which are exactly equivalent to the Wegner model and
to an easier variant.
