Finite and countable sets
Countability includes finite sets in this convention.
Key knowledge
A set is countably infinite if it has a bijection with the natural numbers. Here, countable means finite or countably infinite, equivalently admitting an injection into N.
Conditions and scope
- Fix this inclusive convention; some texts use countable to mean countably infinite.
- This is a cardinality definition, not a claim that every infinite set can be listed.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Axiom list; section 2 separation schema; section 9.6–9.10 finite/countably infinite convention.
2026-10-10 · Definitions 9.6–9.7 and Corollary 9.9 only.
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