Abstract
Formulae describing the electron transport coefficients as functions of the conductivity tensor are derived on the basis of the linear response theory. It is shown that the Wiedemann-Franz law and the Mott rule are obeyed even in the presence of a quantizing magnetic field omega tau >1 if the scattering of electrons is elastic and if h(cross) omega >>kT. As no assumptions about the form of the one-electron potential are made, the conclusions are valid not only in the case of the Shubnikov-de Haas oscillations but also if effects such as magnetic breakdown and the size-effect appear.