  We consider the problem of diffusion-controlled evolution of the system
$A$-particle island - $B$-particle island at propagation of the sharp
annihilation front $A+B\to 0$. We show that this general problem, which
includes as particular cases the sea-sea and the island-sea problems,
demonstrates rich dynamical behavior from self-accelerating collapse of one of
the islands to synchronous exponential relaxation of the both islands. We find
a universal asymptotic regime of the sharp front propagation and reveal limits
of its applicability for the cases of mean-field and fluctuation fronts.
