Kondo effect in the vicinity of a singlet-triplet transition in a vertical
quantum dot is considered. This system is shown to map onto a special versi
on of the two-impurity Kondo model. At any value of the control parameter,
the system has a Fermi-liquid ground state. Explicit expressions for the li
near conductance as a function of the control parameter and temperature T a
re obtained. At T = 0, the conductance reaches the unitary limit similar to
4e(2)/h at the triplet side of the transition, and decreases with the incr
easing distance to the transition at the singlet side. At finite temperatur
e, the conductance exhibits a peak near the transition point.