Alphabeta Math
DefinitionDefinition: Literature-sourcedProof: Not applicableaudited 2026-09-04 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 balanced derived bifunctor

Definition

Assume the Axiom of Dependent Choice. Let A,C,D be abelian categories, let B:Aop×CD be additive in each variable, let P be supplied projective resolution data on a class DA in A, and let I be supplied injective resolution data on a class DC in C. Assume moreover that for each fixed ADA the covariant functor B(A,):CD is left exact, and that for each fixed CDC the functor B(,C):AopD is left exact.

A balanced derived bifunctor relative to (P,I) on DAop×DC consists of the two candidate one-variable right-derived constructions from A bifunctor can be derived in either variable when the relevant resolution data are supplied together with, for every n0, a natural isomorphism RIn(B(A,))(C)RPopn(B(,C))(A) natural in ADA and CDC. These isomorphisms must satisfy:

  1. in degree 0, when the two candidates are identified with B(A,C) by The zero-th right derived functor of a left exact functor recovers the functor on C and on Aop, the balance isomorphism becomes the identity of B(A,C);
  2. the isomorphisms are natural in both variables in the sense of Natural transformation and its components.

This is a definition relative to the displayed supplied data P and I; it does not impose an unquantified condition involving alternative data. The definition records extra comparison data, while the previous proposition only constructs the two candidates.

Depends on

Used by

Dependency tree · two levels

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Sources