PropositionStatement: AI-adaptedProof: AI-generatedPipeline-generatedprecheck passjudge pass (gpt-5.6-terra)audited 2026-09-01‡ 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.

A short exact sequence of complexes gives six-term exact sequences when homology is concentrated in two degrees

Statement

Let $0 \to A_{∙} \to B_{∙} \to C_{∙} \to 0$ be a short exact sequence of complexes in an abelian category. Fix $n \in Z$ , and assume that all three complexes have zero homology outside degrees $n$ and $n - 1$ . Then the long exact sequence collapses to a six-term exact sequence $0 \to H_{n} (A) \to H_{n} (B) \to H_{n} (C) \overset{\partial_{n}}{\to} H_{n - 1} (A) \to H_{n - 1} (B) \to H_{n - 1} (C) \to 0.$

Facts & Assumptions

Given: A short exact sequence of complexes in an abelian category whose homology is concentrated in degrees $n$ and $n - 1$ .

[L1]

Every short exact sequence of complexes yields a long exact homology sequence (The long exact sequence in homology).

Proof

technique · direct

1.1

By [L1], the short exact sequence gives a long exact sequence running through the six displayed terms.

L1givenconstruct

2.1

Every homology term immediately before and after those six terms is zero by the concentration hypothesis. Removing those zero terms leaves the displayed six-term exact sequence.

step 1.1givenalgebra∎

Depends on

The long exact sequence in homology

Used by

Nothing in the library uses this result yet.

Dependency tree · two levels

7 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

Charles A. Weibel, Chapter 1 of An Introduction to Homological Algebra (standard reference, not scraped)