Descent for sheaves on compact Hausdorff spaces

Haine · 2022 · higher-category-theory · 10.48550/arxiv.2210.00186 · record haine2022-descent-for-sheaves-on-compact-hau
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Where this record's text came from. faceted 2026-08 by reading the locally held text (pdftext); every evidence string verified as an exact substring of that text before merging. The paper also contains a genuine null-result strand (the plain sheaf and hypersheaf functors are NOT sheaves on Comp: "Perhaps surprisingly, the answer to Question 0.1 is negative (see Corollary 2.18)."), but the headline contribution is the positive descent theorem, so claim type is recorded as existence. Extraction is clean apart from mathematical-symbol garbling in displayed formulas; all quotes are taken from running prose that survived intact. Author-year metadata comes from the title block, which was not quoted. faceted 2026-08 by reading the locally held text (pdftext); every evidence string verified as an exact substring of that text before merging. The paper also contains a genuine null-result strand (the plain sheaf and hypersheaf functo 2026-08-14 schema-0.3 pass: every quote verified as an exact substring of the staged text and anchored at merge time; concept terms verified present; every edge endpoint an existing node.
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Tags on this paper

Every tag the record carries, each linking to every other paper in the corpus that carries it. A tag appears here whether or not its words occur in the article — the spans below are only the ones a sentence in this paper licenses. Of the 5 concept tags on this paper, all 5 are grounded in a quoted sentence.
hypersheaves Postnikov complete sheaves condensed cohomology compact Hausdorff spaces hypercompleteness Descent fails because every compact Hausdorff space is covered by a profinite set, and sheaves on profinite sets are already Postnikov complete while sheaves on a general compact Hausdorff space are not, so the target of the limit is forced to satisfy a completeness the source lacks. Postnikov completion Postnikov complete proper descent compactly assembled ∞-category hypercomplete objects van Kampen colimit mathematical-proof

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relation to other workclaim_relationshow this paper stands to another: agrees, contradicts, extends, qualifies
claim typeclaim_typethe shape of the claim: existence, mechanism, method, critique, prediction, null
concept edgeconcept_edgesan asserted relation between two concepts, with the sentence asserting it
conceptconceptsan idea the paper works with, quoted where the paper uses it
content tagcontent_tagsa finding, definition, quantity, statistic or variable named in the paper
limitationlimitationswhat the paper says its evidence cannot support
mechanismmechanismshow the reported effect is said to come about
methodmethodhow the paper produced its evidence
phenomenonphenomenonthe effect or regularity under study
sensesensesa distinct use of a term, quoted where the paper fixes it

The paper

The full text is not reproduced here. This article is not cleared for redistribution, so the page carries the tag layer only. Its evidence sentences are withheld; the grounding status remains with each tag, and the article itself is at https://doi.org/10.48550/arxiv.2210.00186. The reading view exists for the papers whose licence permits it.

Every tag on this page

claim_relations 2 · claim_type 1 · concept_edges 1 · concepts 5 · content_tags 15 · limitations 6 · mechanisms 1 · method 1 · phenomenon 1 · senses 3

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facettagfieldconf.whose words
claim_typeexistence
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claim_typethe paper's words
phenomenondescent for sheaves on compact Hausdorff spaces
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phenomenonthe paper's words
methodmathematical-proof
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methodthe paper's words
mechanismsmechanisms
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mechanisms[0]the tagger's words
limitationsThe descent and full-faithfulness results fail before Postnikov completion; the paper devotes sections to explaining why.
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limitations[0]the tagger's words
limitationsWhether every-object-is-the-limit-of-its-Postnikov-tower is strictly weaker than Postnikov completeness is left open.
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limitations[1]the tagger's words
limitationsThe protruncated shape, one of the derived consequences, does not preserve pullbacks.
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limitations[2]the tagger's words
limitationsThree competing sheaf theories agree on all truncated objects, so which one a result used is invisible until unbounded objects are involved.
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what this limits: a result stated for sheaves on a space: sheaves, hypersheaves and Postnikov complete sheaves all have the same truncated objects, and the differences between the three theories appear only on unbounded objects - so two such results can be compared safely in the truncated case and not otherwise
limitations[3]1.0the tagger's words
limitationsTwo incompatible set-theoretic foundations are in use in this literature; the difference is declared inessential and then not mentioned again.
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what this limits: a comparison between results in this paper and results of Clausen and Scholze: the two use different set-theoretic foundations, one with universes and one avoiding them, which the author states is a minor difference not affecting any argument in an essential way
limitations[4]1.0the tagger's words
limitationsThe agreement between three cohomology theories is claimed for spaces satisfying a stated structural condition, not in general.
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what this limits: the claim that condensed and sheaf cohomology agree: the three-way agreement is asserted for a topological space admitting a locally finite CW structure, so it is a conditional identification rather than a general one
limitations[5]1.0the tagger's words
conceptshypersheaves
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also in: hypersheaves
concepts[0]the paper's words
conceptsPostnikov complete sheaves
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concepts[1]the paper's words
conceptscondensed cohomology
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concepts[2]the paper's words
conceptscompact Hausdorff spaces
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concepts[3]the paper's words
conceptshypercompleteness
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concepts[4]the paper's words
sensessheaf theory - THREE OF THEM, DISTINGUISHED ONLY OFF THE TRUNCATED PART: sheaves, hypersheaves and Postnikov complete sheaves all extend the classical theory and share their truncated objects, so the choice between them is undetectable in the bounded case
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senses[0]1.0the tagger's words
sensesthe subject's name - CONDENSED/PYKNOTIC, BOTH CARRIED: the field is written with a slash between two names for it, in a paper by one of the pyknotic authors thanking the condensed ones
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senses[1]1.0the tagger's words
sensesthe set theory - A DIFFERENCE DECLARED AND THEN SET ASIDE: universes here, no universes there, and an explicit decision not to mention it again
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senses[2]1.0the tagger's words
claim_relationsextends → Dyckhoff [7, Theorem 3.11; 8] and Clausen–Scholze [23, Theorem 3.2] comparison of sheaf and condensed cohomology
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claim_relations[0]the tagger's words
claim_relationsbuilds-on → Clausen–Scholze's condensed/pyknotic mathematics, Barwick–Haine, and Lurie's work on ultracategories
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claim_relations[1]the tagger's words
concept_edgesPostnikov complete sheaves —distinct-from→ hypersheaves
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strength of the relation: 1
concept_edges[0]the tagger's words
content_tagsFor a compactly assembled coefficient ∞-category, the assignment of the ∞-category of Postnikov complete sheaves to a locally compact Hausdorff space satisfies descent along proper surjections.
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content_tags.findings[0]the tagger's words
content_tagsThe same result gives proper descent for left complete derived ∞-categories and shows that Postnikov complete sheaves form a sheaf on compact Hausdorff spaces for the topology of finite jointly surjective families.
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content_tags.findings[1]the tagger's words
content_tagsNeither ordinary sheaves nor hypersheaves define a sheaf on the site of compact Hausdorff spaces.
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content_tags.findings[2]the tagger's words
content_tagsPostnikov complete sheaves on a locally compact Hausdorff space embed fully faithfully into condensed objects over that space.
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content_tags.findings[3]the tagger's words
content_tagsConsequently the sheaf cohomology and the condensed cohomology of a locally compact Hausdorff space coincide.
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content_tags.findings[4]the tagger's words
content_tagsFor a space carrying a locally finite CW structure, condensed, singular and sheaf cohomology all coincide.
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content_tags.findings[5]the tagger's words
content_tagsSheaves on a profinite set are Postnikov complete, whereas sheaves on the Hilbert cube are not, so Postnikov completeness is not automatic for compact Hausdorff spaces.
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content_tags.findings[6]the tagger's words
content_tagsThe protruncated shape functor fails to preserve pullbacks of compact Hausdorff spaces.
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content_tags.findings[7]the tagger's words
content_tagsPostnikov completion
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content_tags.definitions[0]the tagger's words
content_tagsPostnikov complete
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content_tags.definitions[1]the tagger's words
content_tagsproper descent
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content_tags.definitions[2]the tagger's words
content_tagscompactly assembled ∞-category
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content_tags.definitions[3]the tagger's words
content_tagshypercomplete objects
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content_tags.definitions[4]the tagger's words
content_tagsvan Kampen colimit
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content_tags.definitions[5]the tagger's words
content_tagsPostnikov complete sheaves
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content_tags.definitions[6]the tagger's words

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