  The ground energy level of an oscillator cannot be zero because of
Heisenberg's uncertainty principle. We use methods from symplectic topology
(Gromov's non-squeezing theorem, and the existence of symplectic capacities) to
analyze and extend this heuristic observation to Liouville-integrable systems,
and to propose a topological quantization scheme for such systems, thus
extending previous results of ours.
