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Complemented subsets#1805

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lowasser wants to merge 5 commits intoUniMath:masterfrom
lowasser:complemented-subsets
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Complemented subsets#1805
lowasser wants to merge 5 commits intoUniMath:masterfrom
lowasser:complemented-subsets

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Starting to build infrastructure based around https://arxiv.org/abs/2207.04000 to make a viable measure theory.

[subtypes](foundation-core.subtypes.md) `A` and `A'` of `X` that are
[apart](measure-theory.apart-subtypes.md).

This definition follows {{#cite Zeuner22}}..
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This definition follows {{#cite Zeuner22}}..
This definition follows {{#cite Zeuner22}}.

Comment on lines +25 to +30
A
{{#concept "complemented subtype" Disambiguation="of a type with apartness" Agda=complemented-subtype-Type-With-Apartness}}
of a type `X` equipped with an
[apartness relation](foundation.apartness-relations.md) is an ordered pair of
[subtypes](foundation-core.subtypes.md) `A` and `A'` of `X` that are
[apart](measure-theory.apart-subtypes.md).
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I find this choice of terminology a bit confusing, since it is certainly not a subtype with a complement, but a subtype equipped with a subtype of its complement. Maybe you can say something more about how these objects should be interpreted and what justifies the name?

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It should also be noted that this concept is not to be confused with "decidable subtypes", i.e., subtypes $X \subseteq A$ such that $(X \cup {(A\setminus X)}) = A$, which appear in the literature under the name "complemented subtype".

`(A, A')` and `(B, B')` of a type equipped with an
[apartness relation](foundation.apartness-relations.md), we define the
[large poset](order-theory.large-posets.md) induced by the relation
`A ≤ B ≔ A ⊆ B ∧ B' ⊆ A'`.
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`A ≤ B ≔ A ⊆ B ∧ B' ⊆ A'`.
`(A ≤ B)((A ⊆ B)(B' ⊆ A'))`.

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