  The upshot of this for our discussion may be stated: ‘there are no physically realistic classical systems which exhibit even ergodicity, and so no physically realistic classical system can exhibit randomness. The baker’s transformation is a mathematical curiosity, but is not a genuine case of randomness without chance, since systems like it are not physically possible.’ This response is premature. There are physically interesting systems to which the KAM theorem does not apply. Open or dissipative systems, those which are not confined to a state space region of constant energy, are one much studied class, because such systems are paradigms of chaotic systems. The hallmarks of a chaotic dissipative system are two (Smith 1998: §1.5):