  We consider how to define a natural probability distribution over worlds
within a simple class of deterministic many-worlds theories. This can help us
understand the typical properties of worlds within such states, and hence
explain the empirical success of quantum theory within a many-worlds framework.
We give three reasonable axioms which lead to the Born rule in the case of
quantum theory, and also yield natural results in other cases, including a
many-worlds variant of classical stochastic dynamics.
