Failure of tensor-product compatibility for supports in Markov categories

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Let C\mathsf{C} be a Markov category with supports, and let pp and qq be morphisms in C\mathsf{C}. Write SfS_f for the support object of a morphism ff. Support tensor-product failure conjecture. There exists such a category and such morphisms for which

Sp⊗q≇Sp⊗Sq.S_{p \otimes q} \not\cong S_p \otimes S_q.

The question concerns whether supports interact well with the monoidal structure. The source states that this remains open, while suggesting that the displayed compatibility need not hold.

References

Primary source

Tobias Fritz, Tomáš Gonda, Antonio Lorenzin, Paolo Perrone and Dario Stein, “Absolute continuity, supports and idempotent splitting in categorical probability”, arXiv:2308.00651 (2026).

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