Compositionality

The open-access journal for the mathematics of composition

Infinite products and zero-one laws in categorical probability

Tobias Fritz1 and Eigil Fjeldgren Rischel2

1Deparment of Mathematical Sciences, University of Copenhagen, 2100 Denmark
2Perimeter Institute for Theoretical Physics, N2L 2Y5, Waterloo, Ontario, Canada

Updated version: The authors have uploaded version v6 of this work to the arXiv which may contain updates or corrections not contained in the published version v5. The authors left the following comment on the arXiv:
20 pages. v6: Some minor fixes

ABSTRACT

Markov categories are a recent category-theoretic approach to the foundations of probability and statistics. Here we develop this approach further by treating infinite products and the Kolmogorov extension theorem. This is relevant for all aspects of probability theory in which infinitely many random variables appear at a time. These infinite tensor products $\bigotimes_{i \in J} X_i$ come in two versions: a weaker but more general one for families of objects $(X_i)_{i \in J}$ in semicartesian symmetric monoidal categories, and a stronger but more specific one for families of objects in Markov categories.

As a first application, we state and prove versions of the zero--one laws of Kolmogorov and Hewitt--Savage for Markov categories. This gives general versions of these results which can be instantiated not only in measure-theoretic probability, where they specialize to the standard ones in the setting of standard Borel spaces, but also in other contexts.

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► References

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