Compact sets #
We define a few types of compact sets in a topological space.
Main Definitions #
For a topological space α,
TopologicalSpace.Compacts α: The type of compact sets.TopologicalSpace.NonemptyCompacts α: The type of non-empty compact sets.TopologicalSpace.PositiveCompacts α: The type of compact sets with non-empty interior.TopologicalSpace.CompactOpens α: The type of compact open sets. This is a central object in the study of spectral spaces.
Compact sets #
The type of compact sets of a topological space.
- carrier : Set α
the carrier set, i.e. the points in this set
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See Note [custom simps projection].
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Reinterpret a compact as a closed set.
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The type of compact sets is inhabited, with default element the empty set.
The image of a compact set under a continuous function.
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A homeomorphism induces an equivalence on compact sets, by taking the image.
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The image of a compact set under a homeomorphism can also be expressed as a preimage.
The product of two TopologicalSpace.Compacts, as a TopologicalSpace.Compacts in the product
space.
The compacts neighbourhoods of a compact
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The compact neighbourhood induced by the existence of an open subset between two compacts
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The set of opens neighbourhood of a compact subset
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The opens neighbourhood of a compact subset that are relatively compact
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The converting map from relatively compact opens neighbourhood of a compact subset to its opens neighbourhoods
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An open relatively compact neighbourhood of K induces a compact neighbourhood by taking
the closure
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The set of compacts inside an open subset
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For K a compact subset inside an open subset U, U has a structure of open neighbourhood
of K
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For U an open neighbourhood of K, K has a structure of compact inside U
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Nonempty compact sets #
The type of nonempty compact sets of a topological space.
- isCompact' : IsCompact self.carrier
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See Note [custom simps projection].
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Reinterpret a nonempty compact as a closed set.
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In an inhabited space, the type of nonempty compact subsets is also inhabited, with default element the singleton set containing the default element.
The image of a nonempty compact set under a continuous function.
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The product of two TopologicalSpace.NonemptyCompacts, as a TopologicalSpace.NonemptyCompacts
in the product space.
TopologicalSpace.NonemptyCompacts.toCompacts as an order embedding.
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Positive compact sets #
The type of compact sets with nonempty interior of a topological space.
See also TopologicalSpace.Compacts and TopologicalSpace.NonemptyCompacts.
- isCompact' : IsCompact self.carrier
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See Note [custom simps projection].
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Reinterpret a positive compact as a nonempty compact.
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The image of a positive compact set under a continuous open map.
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In a nonempty locally compact space, there exists a compact set with nonempty interior.
The product of two TopologicalSpace.PositiveCompacts, as a TopologicalSpace.PositiveCompacts
in the product space.
Compact open sets #
The type of compact open sets of a topological space. This is useful in non-Hausdorff contexts, in particular spectral spaces.
- isCompact' : IsCompact self.carrier
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See Note [custom simps projection].
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Reinterpret a compact open as an open.
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Reinterpret a compact open as a clopen.
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The image of a compact open under a continuous open map.
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The product of two TopologicalSpace.CompactOpens, as a TopologicalSpace.CompactOpens in the
product space.