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category_theory.limits.pi

Limits in the category of indexed families of objects. #

Given a functor F : J ⥤ Π i, C i into a category of indexed families,

  1. we can assemble a collection of cones over F ⋙ pi.eval C i into a cone over F
  2. if all those cones are limit cones, the assembled cone is a limit cone, and
  3. if we have limits for each of F ⋙ pi.eval C i, we can produce a has_limit F instance

A cone over F : J ⥤ Π i, C i has as its components cones over each of the F ⋙ pi.eval C i.

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A cocone over F : J ⥤ Π i, C i has as its components cocones over each of the F ⋙ pi.eval C i.

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Given a family of cones over the F ⋙ pi.eval C i, we can assemble these together as a cone F.

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Given a family of cocones over the F ⋙ pi.eval C i, we can assemble these together as a cocone F.

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Given a family of limit cones over the F ⋙ pi.eval C i, assembling them together as a cone F produces a limit cone.

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Given a family of colimit cocones over the F ⋙ pi.eval C i, assembling them together as a cocone F produces a colimit cocone.

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If we have a functor F : J ⥤ Π i, C i into a category of indexed families, and we have limits for each of the F ⋙ pi.eval C i, then F has a limit.

If we have a functor F : J ⥤ Π i, C i into a category of indexed families, and colimits exist for each of the F ⋙ pi.eval C i, there is a colimit for F.

As an example, we can use this to construct particular shapes of limits in a category of indexed families.

With the addition of import category_theory.limits.shapes.types we can use:

local attribute [instance] has_limit_of_has_limit_comp_eval
example : has_binary_products (I  Type v₁) := by apply_instance