TheoremStatement: Literature-sourcedProof: AI-adaptedPipeline-generatedprecheck passjudge pass (gpt-5.6-terra)audited 2026-09-06‡ 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.

Injective dimension at most n iff higher Ext vanishes

Statement

Assume enough injectives. For an object $N$ and $n \geq 0$ , $id (N) \leq n$ if and only if ${Ext}^{k} (M, N) = 0$ for every object $M$ and every $k > n$ .

Facts & Assumptions

Given: An object $N$ , an integer $n \geq 0$ , and enough injectives.

Proof

technique · direct

1.1

If $id (N) \leq n$ , the $n$ th cosyzygy is injective. Repeated second-variable shifting from Ext dimension shifting in the second variable reduces every ${Ext}^{k} (M, N)$ with $k > n$ to positive Ext into that injective cosyzygy, which vanishes by Positive injective-resolution Ext vanishes on an injective second variable.

givenconstruct

2.1

Conversely, repeated shifting makes ${Ext}^{1} (M, Σ^{n} N)$ vanish for every $M$ . The defining injective-dimension convention in Injective dimension of an object and the splitting criterion for the final cosyzygy show it is injective, so the chosen resolution has length at most $n$ .

step 1.1algebra∎

Depends on

Used by

Global dimension is the supremum of nonzero Ext degrees Theorem

Dependency tree · two levels

9 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, An Introduction to Homological Algebra, Chapters 3–4 (standard reference, not scraped)