  We consider a particular instance of reflection of shock waves in
self-similar compressible flow. We prove that local self-similar regular
reflection (RR) cannot always be extended into a global flow. Therefore the
detachment criterion is not universally correct. More precisely, consider the
following "angle condition": the tangent of the strong-type reflected shock
meets the opposite wall at a sharp or right downstream side angle. In cases
where the condition is violated and the weak-type reflected shock is transonic,
we show that global RR does not exist. Combined with earlier work we have shown
that none of the classical criteria for RR-MR transition is universally
correct. A new criterion is proposed. Moreover, we have shown that strong-type
RR is unstable, in the sense that global RR cannot persist under perturbations
to one side. This yields a definite answer to the weak-strong problem because
earlier work shows stability of weak RR in the same sense.
