Australian Category Seminar

On Hasegawa’s Question about Traced Monoidal Closed Categories and Idempotent Comonads on Compact Closed Categories

JS Lemay·4 November 2026

In Hasegawa's paper “On Traced Monoidal Closed Categories”, he showed that a traced monoidal category was closed if and only if the canonical functor into the its INT construction has a right adjoint. As a consequence, every traced monoidal closed category is a reflexive subcategory of a compact closed category. As such, for a traced monoidal closed category, there is an idempotent comonad on its INT construction. Hasegawa pondered an open question of if there was a possible adjunction between traced monoidal closed categories and compact closed categories with a suitable notion of idempotent comonad. In this talk, I will review the main results of Hasegawa's paper and answer his open question (hopefully correctly!).

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