  We examine the long time behaviour of A+B->0 reaction diffusion systems with
initially segregated species A and B. All of our analysis is carried out for
arbitrary (positive) values of the diffusion constants $D_A$, $D_B$, and
initial concentrations $a_0$ and $b_0$ of A's and B's. We divide the domain of
the partial differential equations describing the problem into several regions
in which they can be reduced to simpler, solvable equations, and we merge the
solutions. Thus we derive general formulae for the concentration profiles
outside the reaction zone, the location of the reaction zone center, and the
total reaction rate. An asymptotic condition for the reaction front to be
stationary is also derived. The properties of the reaction layer are studied in
the mean-field approximation, and we show that not only the scaling exponents,
but also the scaling functions are independent of $D_A$, $D_B$, $a_0$ and
$b_0$.
