DefinitionDefinition: AI-adaptedProof: Not applicablejudge pass (gpt-5.6-terra)audited 2026-08-30‡ rests on unproved material (inherited)

How statement and proof provenance work

The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.

Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
AI-generated: a genuinely novel statement formulated by AI, with no source for the claim itself.

These labels describe origin, not correctness: citations and verification chips remain separate evidence.

‡ Rests on 3 statements not proved in this library, by way of the results it cites. This item cites no such statement directly; it depends on results that do. The unproved premises it inherits are ‡ Cohen's first model: an infinite Dedekind-finite set of reals, ‡ Sierpiński 1947: the generalised continuum hypothesis implies the Axiom of Choice and ‡ The continuum hypothesis and its generalisation are independent of ZFC. Each is recorded with a citation to the literature and is not established here, because the track that would prove it has not yet been developed in this library. Everything else in this proof is proved here.

The arrow category of an abelian category

Definition

Let $[1]$ denote the category with two objects and one nonidentity arrow. For an abelian category $A$ , the arrow category $A^{\to}$ is the functor category $[[1], A]$ .

Thus an object of $A^{\to}$ is a morphism $x : X_{0} \to X_{1}$ in $A$ , and a morphism in $A^{\to}$ is a commutative square between such arrows.

Because $[1]$ is small, this is an honest functor category by Functor category $[C, D]$ and If $C$ is small and $D$ is locally small then $[C, D]$ is locally small; if both are small it is small. Because limits and colimits in a functor category are computed pointwise, an abelian category gives an abelian arrow category as well.

Depends on

Used by

Naturality of the connecting morphism Theorem

Dependency tree · two levels

16 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.

Sources

The Stacks Project, Section 12.5, Lemma 12.5.18 (standard reference, not scraped)
Saunders Mac Lane, Categories for the Working Mathematician, Exercise VIII.4.4 (standard reference, not scraped)