The Λ coend of a pair of functors #
Deligne 3.4's object Λ(α, β): the coend over X of
α(X)∨ ⊗ β(X), built here as the coend of the diagram
(X, Y) ↦ α(Xᘁ) ⊗ β(Y) using the source category's rigidity —
for tensor functors the two agree, and this form needs no duals in
the target. This file provides the diagram, the coend with its
stage maps and dinaturality, the mapping property, and
functoriality in both arguments.
The Λ diagram of a pair of functors: (X, Y) ↦ α(Xᘁ) ⊗ β(Y),
contravariant in X through the adjoint mate.
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Existence of the Λ coend of the pair (α, β).
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The Λ object of a pair of functors: the coend of
(X, Y) ↦ α(Xᘁ) ⊗ β(Y).
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The stage map of the Λ coend at an object of the source.
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- RS.lambdaStage α β X = CategoryTheory.Limits.coend.ι (RS.lambdaDiagram α β) X
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Dinaturality of the stage maps.
Dinaturality of the stage maps.
Maps out of the Λ object agree once they agree on stages.
Descend a dinatural family of maps to the Λ object.
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- RS.lambdaDesc α β f hf = CategoryTheory.Limits.coend.desc f hf
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Natural transformations in both arguments induce a map of Λ diagrams.
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Functoriality of the Λ object in both arguments.
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The right dual of the monoidal unit supplied by the rigid structure — the instance the Λ stages use, which need not be the unit-specific instance.
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The rigid right dual of the monoidal unit is the unit, through the canonical comparison of exact pairings.
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The unit of the Λ object of a pair of lax monoidal functors: the units of the functors into the stage at the monoidal unit, through the comparison of the unit with its rigid dual.
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Maps out of the image of a coend under a colimit-preserving functor agree once they agree on the images of the stages.
Maps out of a tensor by a coend agree once they agree on
whiskered stages, provided tensoring preserves the coend's
colimit presentation. The workhorse for descending
multiplications through Λ ⊗ Λ.
Right-hand mirror of RS.tensorLeft_coend_hom_ext.
The cocone under the whiskered multispan carried by a dinatural family.
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Descend a whiskered dinatural family through a tensor by a coend.
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The cocone under the right-whiskered multispan carried by a dinatural family.
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Descend a right-whiskered dinatural family through a tensor by a coend.
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The braid shuffle: the two ways of carrying the reversed pair across a third object agree — the Yang–Baxter consequence behind the associativity of the Λ multiplication.
Maps into a right dual agree once their evaluation composites agree.
The comparison of the dual of a product with the product of the duals reduces the rigid evaluation to the tensor-pairing evaluation.
The mate of a left whiskering, through the comparison of the dual of a tensor product with the tensor of the duals: the dinaturality input of the Λ multiplication.
The mate of a right whiskering: the left-slot mirror of
RS.whiskerLeft_mate_square.
The mate of the associator, through the comparisons of duals of tensor products: the source-side kernel of the Λ associativity.
Associativity of the composite dual comparisons: the full source-side input of the Λ associativity, assembled from the braid shuffle and the mate of the associator.
The mate of the braiding through the dual-tensor comparisons: the source-side kernel of the Λ commutativity.
The tensor dual comparison at the monoidal unit, pinned to the rigid blanket instances that the Λ stages use.
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The rigid evaluation of the monoidal unit, at the blanket instance.
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The unit comparison reduces the blanket evaluation of the unit to the unit pairing.
The pinned tensor dual comparison at the unit reduces the rigid evaluation to the expanded tensor evaluation.
The tensor dual comparison with the unit on the right, pinned to the rigid blanket instances.
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The pinned tensor dual comparison with the unit on the right reduces the rigid evaluation to the expanded tensor evaluation.
The mate of the right unitor: the mirror of
RS.leftUnitor_mate.
The mate of the left unitor, expressed through the unit and tensor dual comparisons: the source-side input of the Λ unit law.
The stage-level multiplication of the Λ object: middle-four exchange, the tensorators of the two functors, and the comparison of the dual of a product with the product of the duals.
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The stage-level associativity of the Λ multiplication.
Dinaturality of the stage-level multiplication in the right variable: the input of the inner coend descent of the Λ multiplication.
The stage-level left unit computation: the Λ unit composed into the multiplication at a stage collapses to the left unitor.
Dinaturality of the stage-level multiplication in the left variable: the input of the outer coend descent of the Λ multiplication.
The inner descent of the Λ multiplication: for a fixed left stage, the stage-level multiplication descends through the right coend.
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Dinaturality of the inner descent in the left variable.
The Λ multiplication (Deligne 3.7's product): the stage-level multiplication descended through both coend variables.
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- RS.lambdaMul α β = RS.tensorRightCoendDesc (RS.lambdaDiagram α β) (RS.lambdaObj α β) (fun (X : A) => RS.lambdaMulLeft α β X) ⋯
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The two-stage computation of the Λ multiplication.
The left unit law of the Λ algebra: the Λ unit composed into the Λ multiplication is the left unitor.
The stage-level right unit computation: the mirror of
RS.lambdaMulStage_unit_left.
The right unit law of the Λ algebra.
Maps out of the triple tensor of the Λ object agree once they agree on triples of stages.
Associativity of the Λ multiplication (Deligne 3.8).
Maps out of the square of the Λ object agree once they agree on pairs of stages.
The Λ algebra (Deligne 3.7): the coend of a pair of lax monoidal functors from a braided rigid source is a monoid object, with the stage at the unit as unit and the descended stage-level multiplication as product.
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- RS.lambdaMonObj α β = { one := RS.lambdaUnit α β, mul := RS.lambdaMul α β, one_mul := ⋯, mul_one := ⋯, mul_assoc := ⋯ }
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The stage-level multiplication is natural in the pair of monoidal transformations.
The stage-level commutativity of the Λ multiplication over a symmetric source and target with braided functors.
Commutativity of the Λ multiplication (Deligne 3.8).
The Λ algebra is commutative over symmetric data with braided functors (Deligne 3.7–3.8 in full).