Title: The combinatorics of
Hamiltonian circle actions.
Abstract: When a large torus
acts on a symplectic manifold, it is often
possible to show
the important geometrical properties are encoded,
sometimes almost
magically, by simple combinatorical objects.
For circle
actions, the situation is more complicated; nevertheless,
it may be
possible to also answer many questions by by similar
simple
computations in this case.