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.
FALSE: every abelian category has enough projectives and enough injectives
Statement
False. Every abelian category has enough projectives and enough > injectives.
Facts & Assumptions
Given: The abelian category of finite abelian groups.
Enough projectives and enough injectives are extra hypotheses, not part of the definition of abelian category (A category with enough projectives and with enough injectives).
The projective-resolution construction on this page still needs a chosen projective epimorphism at each stage (A chosen chain of projective epimorphisms gives a projective resolution).
The Grothendieck theorem gives enough injectives only under additional Grothendieck hypotheses (Every Grothendieck category has enough injectives, and every object admits an injective resolution).
Refutation
The category is abelian. If it had enough projectives in the sense of [L1], then some nonzero projective object would surject onto for some prime . Choose a cyclic quotient with maximal among all cyclic -power quotients of .
The canonical quotient is epic. If were projective, would lift across , producing a surjection , contradicting maximality of . So does not have enough projectives, and the universal statement is false. The positive statements [L2] and [L3] are therefore extra-hypothesis results, not automatic consequences of abelianity.
Depends on
Used by
Nothing in the library uses this result yet.
Dependency tree · two levels
10 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
- The Stacks Project, Section 19.11: Injectives in Grothendieck categories (standard reference, not scraped)
- Romyar Sharifi, Homological Algebra (standard reference, not scraped)