  We have calculated the thermoelectric conductivity tensor $\varepsilon_{ij}$
and the thermal conductivity tensor $\lambda_{ij}$ of a unidirectional lateral
superlattice (ULSL) ($i,j = x,y$, with the $x$-axis aligned to the principal
axis of the ULSL), %, given as the first- and the second-order moments,
employing based on the asymptotic analytic formulas of the electrical
conductivity tensor $\sigma_{ij}$ in the literature valid at low magnetic
fields where large numbers of Landau levels are occupied. With the resulting
analytic expressions, we clarify the conditions for the Mott formula
(Wiedemann-Franz law) to be applicable with high precision to
$\varepsilon_{ij}$ ($\lambda_{ij}$). We further present plots of the
commensurability oscillations $\delta\varepsilon_{ij}$, $\delta\lambda_{ij}$,
$\delta\kappa_{ij}$, and $\delta S_{ij}$ in $\varepsilon_{ij}$, $\lambda_{ij}$,
(an alternative, more standard definition of) the thermal conductivity tensor
$\kappa_{ij}$, and the thermopower tensor $S_{ij}$, calculated using typical
parameters for a ULSL fabricated from a GaAs/AlGaAs two-dimensional electron
gas (2DEG). Notable features of the $\delta S_{ij}$ are (i) anisotropic
behavior ($\delta S_{xx} \ne \delta S_{yy}$) and (ii) the dominance of the $xy$
component over the other components ($|\delta S_{xy}| \gg |\delta S_{yx}|,
|\delta S_{xx}|, |\delta S_{yy}|$). The latter clearly indicates that the two
Nernst coefficients, $S_{xy}$ and $S_{yx}$, can be totally different from each
other in an anisotropic system. Both (i) and (ii) are at variance with the
previous theory and are attributable to the inclusion of a damping factor due
to the small-angle scattering characteristic of GaAs/AlGaAs 2DEGs, which have
not been taken into consideration in $\delta S_{ij}$ thus far.
