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Canonical static concept record

Cardinal

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Summary

An initial ordinal used to represent the size of a set.

Record metadata

Carrier(s)

Axioms / constraints

Notes

A cardinal is an initial ordinal. In ZF this represents the size of any well-orderable set; assigning a cardinal to every set is equivalent to the well-ordering principle and hence to the axiom of choice.

Concept sources

Incoming relations (arrows to this concept)

Each relation below ends at this concept.

OrdinalCardinal

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This is an authored directed relation from the source endpoint to the target endpoint.

Authored explanation

Require the ordinal to have no equipotent smaller ordinal.

How to interpret this relation type

Keep the existing data and select the subclass satisfying an additional law, existence condition, finiteness condition, or other property.

Relation sources

Well-ordering theoremCardinal

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This is an authored directed relation from the source endpoint to the target endpoint.

Authored explanation

A well-order on a set has a unique ordinal order type; its least equipotent ordinal is the set’s cardinal.

How to interpret this relation type

Record a genuine theorem implication that is not part of the target definition; these edges may point toward a weaker structure.

Relation sources

Outgoing relations (arrows from this concept)

Each relation below starts at this concept.

CardinalCountable infinity 0\aleph_0

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This is an authored directed relation from the source endpoint to the target endpoint.

Authored explanation

0\aleph_0 is the first infinite cardinal.

How to interpret this relation type

The target is a member or subtype of the broader source class.

Relation sources

CardinalFinite cardinal

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This is an authored directed relation from the source endpoint to the target endpoint.

Authored explanation

Finite cardinals are the finite initial ordinals.

How to interpret this relation type

The target is a member or subtype of the broader source class.

Relation sources

CardinalInfinite cardinal

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This is an authored directed relation from the source endpoint to the target endpoint.

Authored explanation

Infinite cardinals are the nonfinite initial ordinals.

How to interpret this relation type

The target is a member or subtype of the broader source class.

Relation sources

CardinalLarge cardinal

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This is an authored directed relation from the source endpoint to the target endpoint.

Authored explanation

Select cardinals satisfying additional closure, compactness, measure, or elementary-embedding properties.

How to interpret this relation type

Keep the existing data and select the subclass satisfying an additional law, existence condition, finiteness condition, or other property.

Relation sources

CardinalLimit cardinal

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This is an authored directed relation from the source endpoint to the target endpoint.

Authored explanation

Limit cardinals are infinite cardinals that are not successors.

How to interpret this relation type

The target is a member or subtype of the broader source class.

Relation sources

CardinalSuccessor cardinal

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This is an authored directed relation from the source endpoint to the target endpoint.

Authored explanation

For each cardinal κ\kappa, well-order the cardinals above it and take the least one, denoted κ+\kappa^+.

How to interpret this relation type

Apply a standard functorial or canonical construction whose output is not merely a reduct of the input and is not generally an equivalent presentation of the same object.

Relation sources