  The usual Heisenberg uncertainty relation for position and momentum may be
replaced by an exact equality, for suitably chosen measures of position and
momentum uncertainty. This "exact" uncertainty relation is valid for_all_ pure
states, and is sufficiently strong to provide an axiomatic basis for moving
from classical mechanics to quantum mechanics. In particular, the assumption of
a nonclassical momentum fluctuation, having a strength which scales inversely
with uncertainty in position, leads from the classical equations of motion to
the Schroedinger equation.
