for the field direction shown in Fi

for the field direction shown in Fig. 87, while Eq. (4.12) is recovered for the other field direction. The observation in the experiment of Fig. 86 for Vg = −2.5V of a regular longitudinal resistance [in agreement with Eq. (4.12)], along with an anomalous quantum Hall resistance is thus consistent with this analysis. The experiments426,429 discussed in the following subsection are topologically equivalent to the geometry of Fig. 87, but involve quantum point contacts rather than ohmic contacts. This gives the possibility of populating and detecting edge channels selectively, thereby enabling a study of the effects of a nonequilibrium population of edge channels in a controlled manner.