  Every quantum physical system can be considered the ''shadow'' of a special
kind of classical system. The system proposed here is classical mainly because
each observable function has a well precise value on each state of the system:
an hypothetical observer able to prepare the system exactly in an assigned
state and able to build a measuring apparatus perfectly corresponding to a
required observable gets always the same real value. The same system considered
instead by an unexpert observer, affected by the ignorance of a hidden
variable, is described by a statistical theory giving exactly and without
exception the states, the observables, the dynamics and the probabilities
prescribed for the usual quantum system.
