Formulate codereliction axioms purely within monoidal category theory
Determine whether the axioms defining a codereliction transformation can be expressed entirely using the standard structures and concepts of monoidal category theory, without introducing additional ad hoc invertible 2-cells or extra coherence data. This would provide a formulation of codereliction that does not rely on auxiliary diagrams beyond monoidal categorical primitives.
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The definition of a codereliction presented additional problems, in that it is not known whether its axioms can be expressed purely in terms of the basic concepts of the theory of monoidal categories. For this reason, if we were to require the presence of invertible 2-cells in the diagrams that are part of the definition of a codereliction transformation in [BluteR:difcr], we would then be facing the question of what coherence axioms to impose on them, which appears to be a difficult question.