  The unsymmetric confinement of the electrons in a typical 2-dimensional
electron gas (2DEG) breaks the full cubic symmetry of the in-plane transport
properties. A rigorous invariance of the transport under rotation by pi/2 about
the cubic axis perpendicular to the plane of the gas no longer holds, even for
structurally perfect samples, and asymmetries under rotation by pi/2 are
allowed. It is proposed that this symmetry breaking plays a role in the recent
observation, by Little et al., of the pronounced anisotropy of the
magnetoresistance of a 2DEG at very low temperatures, at large half-integer
filling factors of the Landau levels in such a system.
