ExampleConstruction: AI-adaptedVerification: AI-generatedPipeline-generatedprecheck passaudited 2026-08-31‡ 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 mapping cylinder of an inclusion of two-term complexes

Example

Let $C_{∙} = Z [0]$ and let $D_{∙}$ be the two-term complex $0 \to Z \overset{1}{\to} Z \to 0,$ with the right copy in degree $0$ . The inclusion $f : C_{∙} \to D_{∙}$ into degree $0$ has mapping cylinder $Cyl (f)_{1} ≅ Z \oplus Z, Cyl (f)_{0} ≅ Z \oplus Z,$ with differentials read directly from the cylinder formula, and the projection $p : Cyl (f) \to D$ is a homotopy equivalence.

Facts & Assumptions

Given: The inclusion $f : Z [0] \to (0 \to Z \overset{1}{\to} Z \to 0)$ .

[L1]

The mapping-cylinder terms and differential are given explicitly by The mapping cylinder of a chain map.

[L2]

The mapping cylinder factors a chain map through a homotopy equivalence (The mapping cylinder factors a chain map).

Verification

technique · direct

1.1

Applying [L1] degreewise leaves the displayed two copies of $Z^{2}$ in degrees $1$ and $0$ ; all other terms vanish.

L1givenalgebra

2.1

The same construction comes with maps $i$ and $p$ , and [L2] identifies $p$ as a chain-homotopy equivalence. So this example is an explicit two-term instance of the general factorization theorem.

L2step 1.1algebra∎

Depends on

Used by

Nothing in the library uses this result yet.

Dependency tree · two levels

17 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)