In magnetic field, the charged particle cannot
gain or lose energy. Reminder: equalenergy lines in the
simple 2dim band model: from circles to squares.
The evaluation of closed curve motion. This is closed curve in
kspace, can be spiral in xspace. Line, i.e. curve,
which is a cut of Fermi surface by a plane perpendicular to the
magnetic field direction. Use the semiclassic equations
of motion. Time intervals, path intervals on the Fermi curve.
