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.
Cohomological dimension relative to a sheaf class
Definition
Assume the Axiom of Choice (The Axiom of Choice). Let be a topological space, let be a class of sheaves of abelian groups on (that is, a subclass of the objects of , for example the class of all abelian sheaves, or a class of sheaves of modules over a fixed sheaf of rings), and let be sheaf cohomology relative to the supplied functorial injective resolution datum (Sheaf cohomology as right derived global sections). The cohomological dimension of relative to is the infimum of the empty set of integers being . Thus:
- if and only if for every and every ; the value means that for every integer the class contains a sheaf with for some ;
- if for some , then . If this value is finite, the infimum is attained and , the least nonnegative integer with the vanishing property. If there is no finite uniform bound, then and the infimum is not attained;
- exactly when for every and every ; in particular for every class on the empty space, since is the one-element group and is exact (A set-valued sheaf has a unique section over the empty open set, An exact functor has vanishing positive derived functors);
- whenever ; when is the class of all abelian sheaves on one writes for and calls it the cohomological dimension of ;
- the definition is independent of the supplied resolution datum up to the canonical isomorphisms of Sheaf cohomology as right derived global sections, so depends on and only.
In degree zero the vanishing hypothesis in item 2 is satisfied by any class containing a sheaf with a nonzero global section, by Degree-zero sheaf cohomology is global sections.
Depends on
Used by
Dependency tree · two levels
18 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, Cohomology of Sheaves (standard reference, not scraped)