Failure of tensor-product compatibility for supports in Markov categories

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

Spq≇SpSq.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.

Sources & referencesView supporting material

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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