  Using the quasiclassical Green's function in the Coulomb field, we analyze
the probabilities of single and multiple $e^+e^-$-pair production at fixed
impact parameter $b$ between colliding ultrarelativistic heavy nuclei. We
perform calculations in the Born approximation with respect to the parameter
$Z_B\alpha$, and exactly in $Z_A\alpha$, $Z_{A}$ and $Z_{B}$ are the charge
numbers of the corresponding nuclei. We also obtain the approximate formulas
for the probabilities valid for $Z_A\alpha, Z_B\alpha\lesssim 1$.
