Weighted limits #
In this file, we define weighted limits (in the non enriched case).
Given a weight W : J ⥤ Type w and a functor F : J ⥤ C,
the W-weighted limit of J is the limit of the functor
CategoryOfElements.π W ⋙ F : W.Elements ⥤ C.
References #
- https://ncatlab.org/nlab/show/weighted+limit
Given W : J ⥤ Type w and F : J ⥤ C, this is the type of cones for
the functor CategoryOfElements.π W ⋙ F : W.Elements ⥤ C.
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Given a weight W : J ⥤ Type w and F : J ⥤ C, we say that
the W-weighted limit of F exists if the functor
CategoryOfElements.π W ⋙ F : W.Elements ⥤ C has a limit.
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The projection c.pt ⟶ F.obj j for c : WeightedCone W F
and x : W.obj j.
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- c.π x = c.π.app (W.elementsMk j x)
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Constructor for weighted cones.
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A weighted cone c : WeightedCone W F is a limit if it is so
as a cone of CategoryOfElements.π W ⋙ F : W.Elements ⥤ C.
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Constructor for morphisms from the point of a limit weighted cone.
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- hc.lift π hπ = hc.lift (CategoryTheory.Limits.WeightedCone.mk Z π hπ)
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Helper definition in order to show that a weighted cone is a limit.
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- CategoryTheory.Limits.WeightedCone.IsLimit.mk lift fac uniq = { lift := lift, fac := ⋯, uniq := ⋯ }
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If the weight is coyoneda.obj (op j) : J ⥤ Type _, this is the limit
weighted cone for F : J ⥤ C with point F.obj j.
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- CategoryTheory.Limits.WeightedCone.coyoneda F j = CategoryTheory.Limits.WeightedCone.mk (F.obj j) (fun (j' : J) (f : (CategoryTheory.coyoneda.obj (Opposite.op j)).obj j') => F.map f) ⋯
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The weighted limit of F for the weight coyoneda.obj (op j) is F.obj j.
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- One or more equations did not get rendered due to their size.
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Given a weight W : J ⥤ Type w and F : J ⥤ C, this is the W-weighted
limit of F.
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The projections from the weighted limit.
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- W.weightedLimObjObjπ F x = CategoryTheory.Limits.limit.π ((CategoryTheory.CategoryOfElements.π W).comp F) (W.elementsMk j x)
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A choice of limit weighted cone.
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- W.weightedLimCone F = CategoryTheory.Limits.WeightedCone.mk (W.weightedLimObjObj F) (fun (j : J) (x : W.obj j) => W.weightedLimObjObjπ F x) ⋯
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The weighted cone W.weightedLimCone F is a limit.
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Functoriality of the weighted limits with fixed weight W : J ⥤ Type w
with respect to the functor in J ⥤ C.
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The (contravariant) functoriality of weighted limits with respect to the weight.
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- CategoryTheory.Functor.weightedLimFlipObjMap g F = (W.isLimitWeightedLimCone F).lift (fun (j : J) (x : W.obj j) => W'.weightedLimObjObjπ F ((CategoryTheory.ConcreteCategory.hom (g.app j)) x)) ⋯
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Given a weight W : J ⥤ Type w, this is the property that all W-weighted limits
exist for functors F : J ⥤ C. Under this condition, we define a weighted limit functor
W.weightedLimObj : (J ⥤ C) ⥤ C. (See also HasWeightedLimFlipObj for the "flipped"
property for F : J ⥤ C.)
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- W.HasWeightedLimObj C = ∀ (F : CategoryTheory.Functor J C), CategoryTheory.Limits.HasWeightedLimit W F
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Weighted limits for a fixed weight W : J ⥤p Type w, as a functor (J ⥤ C) ⥤ C.
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Given a functor F : J ⥤ C, this is the property satisfied by weights W : J ⥤ Type w
such that the W-weighted limit of F exists.
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Given a functor F : J ⥤ C, this is the functor which sends a weight W : J ⥤ Type w
to the W-weighted limit of F. This is defined on the full subcategory of J ⥤ Type w
where this weighted limit exists.
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Given F : J ⥤ C, this is the property that weighted limits of F exist for all
weights W : J ⥤ Type w. Under this condition, we define a weighted limit functor
F.weightedLimFlipObj : (J ⥤ Type w)ᵒᵖ ⥤ C. (See also HasWeightedLimObj for
the "flipped" property for W : J ⥤ Type w.)
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- F.HasWeightedLimFlipObj = ∀ (W : CategoryTheory.Functor J (Type ?u.5)), CategoryTheory.Limits.HasWeightedLimit W F
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Given a functor F : J ⥤ C, this is the functor (J ⥤ Type w)ᵒᵖ ⥤ C which sends
a weight W : J ⥤ Type w to the W-weighted limit of F. Here, we assume that
all such weighted limits exist.
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When HasWeightedLimFlipObj.{w} F holds, the composition
of the equivalence F.hasWeightedLimit.ι.op with weightedLimFlipObj.{w} F
identifies to weightedLimFlipObj'.{w} F.
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When HasWeightedLimFlipObj.{w} F holds, the composition
of the inverse of the equivalence F.hasWeightedLimit.ι.op with
weightedLimFlipObj'.{w} F identifies to weightedLimFlipObj.{w} F.
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When all weighted limits exists, this is the weighted limit
bifunctor (J ⥤ Type w)ᵒᵖ ⥤ (J ⥤ C) ⥤ C.
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The isomorphism weightedLimObjObj W F ≅ c.pt when c : WeightedCone W F
is a limit.
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Let j : J, the weighted limit functor with weight coyoneda.obj (op j) : J ⥤ Type _
identifies to the evaluation functor (J ⥤ C) ⥤ C at j.
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