  A numerical renormalization group (NRG) investigation of the one-centre
$t-t'$ Kondo problem is performed for the square lattice with account of
logarithmic Van Hove singularities (VHS) in the electron density of states. The
magnetic susceptibility, entropy and specific heat are calculated. The
temperature dependences of the thermodynamic properties in the presence of VHS
turn out to be non-trivial. For finite $t'$ inverse logarithm of the
corresponding Kondo temperature $T_K$ demonstrates a crossover from the
square-root to standard linear dependence on the $s-d$ exchange coupling. The
low-temperature behavior of magnetic susceptibility and linear specific heat
are investigated, and the Wilson ratio is obtained. For $t' -> 0$ the
Fermi-liquid behavior is broken.
