  We present a canonical way of assigning to each magnitude of a classical
mechanical system a differential operator in the configuration space, thus
rigorously establishing the Correspondence Principle for such systems. Here we
show how each classical state given in the whole system determine, for each
classical magnitude, a wave equation, whose solutions are the possible quantum
states for the given state and classical magnitude. Classical states and
quantum states corresponding with the same system are reciprocally conditioned.
