  In previous work (astro-ph/0306228) we have established that a particular
quasi-classical theoretical viewpoint about the nature of gravitation in galaxy
discs provides extremely high concordance (comparable with MOND) with the
observed dynamics in optical discs.
  In this paper, we consider the possibility that the optical disc and the flat
radio disc represent distinct dynamical regions which are inherently described
by distinct phases of the same over-arching theory of which the quasi-classical
theory is but one phase. This is a defining moment for the theory under
discussion since the only natural generalization available is that from the
existing quasi-classical (one-clock) model into a quasi-relativistic
(two-clock) model. The quasi-relativistic disc turns out to be a stationary
hyperbolic disc within which information propagates along characteristics and
within which the rotation curve is necessarily exactly flat.
  The transition between the two components of the disc is managed by
physically determined jump conditions which are represented by a set of
non-linear algebraic equations. These equations predict the existence of a
forbidden region within the parameter space which coincides exactly with that
part of the parameter space in which there is an already observed highly
significant underpopulation of galaxy discs (astro-ph/0107300).
