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LeanPool.RegtsSevenster.RS.Classical.Deligne.ModDual

The dual of a module object #

Substrate for Deligne (2002), §2.8: over a monoidal category D, an exact pairing (X, Y) transports a module structure on X (for a monoid object A) to its dual Y.

Zigzag identities at the modTensor level, and nonvanishing of the copairing, need the multi-tensor coherence layer and are outside this module's scope.

The coevaluation twisted by the action: informally a ↦ (a • xᵢ) ⊗ yᵢ in dual-basis notation.

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    The contragredient right action on the dual: informally f ⊗ a ↦ f (a • ·), that is, f ⊗ a ↦ f (a • xᵢ) yᵢ in dual-basis notation.

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      The dual left action: the contragredient right action pulled back along the inverse braiding. The inverse braiding (rather than the braiding β_ A Y) is chosen so that the braided right action actRight derived from it is exactly dualActRight; see actRight_dualMod.

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        @[implicit_reducible]

        The dual module structure on Y, for a commutative monoid.

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          @[reducible]

          The dual of a module, bundled: Y with the transported action.

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            On the dual module the braided right action is exactly the contragredient right action.

            @[reducible]

            A module object, bundled as a module.

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              The A-valued pairing on the module tensor of the dual with the module: the descent of ε_ X Y ≫ η[A] through the coequalizer. It is balanced but, for a general module, not a morphism of A-modules; see whiskerLeft_modTensorπ_act_modPairing for the equivariance it does satisfy.

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                The copairing into the module tensor of the module with its dual: the twisted coevaluation followed by the projection.

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                  Equivariance of the pairing: acting on the tensor product and pairing equals braiding the scalar through and pairing against the acted-on module. For a general module this is the strongest compatibility available; the pairing is not A-linear.