  A hypercritical value for the magnetic field is determined, which provides
the full compensation of the positronium rest mass by the binding energy in the
maximum symmetry state and disappearance of the energy gap separating the
electron-positron system from the vacuum. The compensation becomes possible
owing to the falling to the center phenomenon. The structure of the vacuum is
described in terms of strongly localized states of tightly mutually bound (or
confined) pairs. Their delocalization for still higher magnetic field, capable
of screening its further growth, is discussed.
