ExampleConstruction: AI-generatedVerification: AI-generatedprecheck passaudited 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 connecting morphism computed for a short exact sequence of abelian groups

Example

In $A b$ , consider

diagram failed to render:
0 \arrow[r] & \mathbb Z \arrow[r, "\times 2"] \arrow[d, "\times 2"'] & \mathbb Z \arrow[r] \arrow[d, "\times 2"'] & \mathbb Z/2 \arrow[r] \arrow[d, "0"'] & 0 \\
0 \arrow[r] & \mathbb Z \arrow[r, "\times 2"'] & \mathbb Z \arrow[r] & \mathbb Z/2 \arrow[r] & 0.

The connecting morphism $δ : \ker (0) ≅ Z / 2 ⟶ coker (\times 2) ≅ Z / 2$ is the identity map.

Facts & Assumptions

Given: The diagram above in $A b$ .

[L1]

Abelian groups form an abelian category (Abelian groups form an abelian category).

[L2]

The connecting morphism exists, and the snake sequence is exact (The connecting morphism exists and is unique, Snake lemma in an abelian category).

Verification

1.1

By [L1], the displayed diagram is valid snake data. Its kernel and cokernel terms are $\ker (\times 2) = 0, \ker (0) = Z / 2, coker (\times 2) = Z / 2.$

L1algebra

2.1

The snake sequence from [L2] therefore reduces to $0 \to 0 \to 0 \to Z / 2 \overset{δ}{\to} Z / 2 \to Z / 2 \to Z / 2 \to 0.$ Exactness at the source and target of $δ$ forces $δ$ to be both injective and surjective, hence the identity automorphism of $Z / 2$ .

L2step 1.1algebra

3.1

So in this concrete diagram the connecting morphism is the identity on $Z / 2$ .

step 2.1∎

Depends on

Used by

Nothing in the library uses this result yet.

Dependency tree · two levels

22 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

Saunders Mac Lane, Categories for the Working Mathematician, Lemma VIII.4.5 (standard reference, not scraped)