  Quantum mechanics for a four-state-system is derived from classical
statistics. Entanglement, interference, the difference between identical
fermions or bosons and the unitary time evolution find an interpretation within
a classical statistical ensemble. Quantum systems are subsystems of larger
classical statistical systems, which include the environment or the vacuum.
They are characterized by incomplete statistics in the sense that the classical
correlation function cannot be used for sequences of measurements in the
subsystem.
