Finite frequentism explains quantum probability

I show that frequentism, as an explanation of probability in classical statistical mechanics, can be extended in a natural way to a decoherent quantum history space, the analogue of a classical phase space. The result is a form of finite frequentism, in which the Gibbs concept of an infinite ensemble of gases is replaced by the quantum state expressed as a superposition of a finite number of decohering microstates. It is a form of finite and actual (as opposed to hypothetical) frequentism insofar as all the microstates exist, even though they may differ macroscopically, in keeping with the decoherence-based Everett interpretation of quantum mechanics.
Comment: 29 pages, 4 figures