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Projective comparison maps are unique up to chain homotopy
Statement
Assume the Axiom of Dependent Choice.
Any two augmentation-preserving maps between projective resolutions lifting the same object morphism are chain-homotopic.
Facts & Assumptions
Given: Two augmentation-preserving maps between projective resolutions, lifting the same object morphism .
A partial comparison homotopy extends one degree at a time (Extending a partial comparison homotopy by one degree).
The maps and are comparison maps in the sense of Augmentation-preserving maps of projective resolutions.
Dependent choice licenses the countable successor-by-successor selection of compatible homotopy components (The axiom of dependent choice: a relation in which every element is related to something admits an -indexed chain).
Proof
Start at degree . Because and lift the same object map, [L1] produces . Every partial homotopy through degree extends one degree further by [L1], and the successive choices depend on the previously chosen components. Therefore [L3] produces a family in every degree.
By construction, the family satisfies the defining chain-homotopy equation in every degree. Therefore and are chain-homotopic.
Depends on
Used by
- Ext can be computed from any projective resolution of the first variable Corollary
- The balanced Ext bifunctor Definition
- An explicit comparison homotopy Example
- Independence of two comparison lifts on homology Example
- FALSE: a comparison map between resolutions is unique as a chain map False statement
- Double bar comparison for cyclic bimodule tensor products Lemma
- minimal free resolutions unique up to chain isomorphism Lemma
- The change-of-projective-resolution isomorphisms are natural Lemma
- The Ext balance isomorphism is independent of resolution comparison data Lemma
- The induced homology map is independent of the chosen comparison lift Lemma
- The left derived connecting map is independent of the horseshoe resolution and lifts Lemma
- Change-of-projective-resolution isomorphisms satisfy identity and cocycle laws Proposition
- Comparison maps respect composition up to homotopy Proposition
- Each resolution-defined Tor construction is covariant in both variables Proposition
- Ext balance isomorphisms satisfy change-of-resolution cocycle laws Proposition
- Horseshoe resolutions are compatible with morphisms of short exact sequences up to homotopy Proposition
- Projective-resolution Ext has the stated bifunctor variance Proposition
- The Tor balance isomorphism is natural and coherent under a change of resolutions Proposition
- Higher Yoneda Ext agrees with derived Ext Theorem
- Hochschild hyperhomology is independent of a projective resolution Theorem
- Injective comparison maps are unique up to cochain homotopy Theorem
- Left derived functors relative to supplied data are additive functors Theorem
- Projective resolutions of the same object are homotopy equivalent over that object Theorem
- The left and right projective constructions of Tor are naturally isomorphic Theorem
Dependency tree · two levels
24 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 (standard reference, not scraped)
- Romyar Sharifi, Homological Algebra (standard reference, not scraped)