  It is sometimes stated that Gleason's theorem prevents the construction of
hidden-variable models for quantum entities described in a more than
two-dimensional Hilbert space. In this paper however we explicitly construct a
classical (macroscopical) system that can be represented in a three-dimensional
real Hilbert space, the probability structure appearing as the result of a lack
of knowledge about the measurement context. We briefly discuss Gleason's
theorem from this point of view.
