  Based on a thermodynamic approach, we have calculated the resistivity of a 2D
electron gas, assumed $dissipationless$ in a strong quantum limit. Standard
measurements, with extra current leads, define the resistivity caused by a
combination of Peltier and Seebeck effects. The current causes heating(cooling)
at the first(second) sample contacts, due to the Peltier effect. The contact
temperatures are different. The measured voltage is equal to the Peltier
effect-induced thermoemf which is linear in current. As a result, the
resistivity is non-zero as $I\to 0$. The resistivity is a universal function of
magnetic field and temperature, expressed in fundamental units $h/e^{2}$. The
universal features of magnetotransport data observed in experiment confirm our
predictions.
