  A fundamental premise of Hamiltonian chaos is the existence and properties of
tori in phase space. More than a geometrical construct, these structures
underlie the very dynamics of both classical and quantal systems. Although
presented in many introductory textbooks on nonlinear dynamics, the structure
of tori in phase space is rarely as transparent as is often presented. Here we
outline some of the mathematics of the tori and illustrate a few of the
geometric and topologically idiosyncrasies.
