Recognition: 2 theorem links
· Lean TheoremOn Galois categories and condensed contractible schemes
Pith reviewed 2026-05-12 04:54 UTC · model grok-4.3
The pith
The condensed fundamental group of Spec(Z) is non-trivial, so the spectrum of the integers is not condensed contractible.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Extending the condensed Galois category of a scheme and describing it via w-contractible rings and ultracategories yields a classification of schemes with initial or terminal objects in their Galois category, implying trivial condensed homotopy type, together with an explicit formula for the condensed fundamental group of a general Dedekind domain; this group is non-trivial when the domain is the integers, so Spec(Z) is not condensed contractible.
What carries the argument
The condensed Galois category of a scheme, extended from prior work and described in terms of w-contractible rings and Lurie's ultracategories, which classifies objects with initial or terminal objects and computes the condensed fundamental group.
If this is right
- Schemes whose condensed Galois category has an initial or terminal object have trivial condensed homotopy type.
- The condensed fundamental group of any Dedekind domain is given by a concrete formula.
- Spec(Z) is not condensed contractible.
- The condensed homotopy type of a scheme is determined by the existence of initial or terminal objects in its Galois category.
Where Pith is reading between the lines
- The distinction between condensed and classical homotopy types may be visible already at the level of the fundamental group for arithmetic schemes.
- The same methods could be applied to compute condensed fundamental groups of other number rings or to compare with pro-etale homotopy types.
- Non-contractibility of Spec(Z) suggests that condensed homotopy theory retains arithmetic information that would be lost if every scheme were treated as contractible.
Load-bearing premise
The extension of the condensed Galois category to schemes and Dedekind domains continues to satisfy the expected formal properties of Galois categories.
What would settle it
An explicit calculation of the condensed fundamental group of Spec(Z) that returns the trivial group rather than a non-trivial one.
read the original abstract
We extend the study of the condensed Galois category of a scheme introduced by Barwick, Glasman and Haine in their work on Exodromy. We elaborate its connection to Lurie's work on Ultracategories and provide a description in terms of w-contractible rings. We give a classification of schemes whose Galois category has an initial, respectively, a terminal object. This implies the condensed homotopy type of the scheme, which was studied in more detail in [arXiv:2510.07443v1], to be trivial. Furthermore, we compute a formula for the (underlying group of the) condensed fundamental group of a general Dedekind domain and show that it is non-trivial for the spectrum of the integers Spec(Z).This means that Spec(Z) is not condensed contractible.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript extends the condensed Galois category of schemes from Barwick-Glasman-Haine by connecting it to Lurie's ultracategories and providing a description in terms of w-contractible rings. It classifies schemes whose Galois categories have initial or terminal objects (implying trivial condensed homotopy types) and derives an explicit formula for the underlying group of the condensed fundamental group of a general Dedekind domain, proving this group is non-trivial for Spec(Z) and hence that Spec(Z) is not condensed contractible.
Significance. If the w-contractible ring description faithfully reproduces the original condensed Galois category (including morphisms and Galois actions) and the formula is correctly derived, the work would supply a concrete computational tool for condensed fundamental groups of Dedekind domains and establish a non-trivial condensed homotopy type for Spec(Z). This strengthens the structural theory of condensed Galois categories and provides a concrete counterexample to contractibility for the most basic arithmetic scheme, with potential implications for exodromy and condensed homotopy in arithmetic geometry.
major comments (3)
- [Description of the condensed Galois category via w-contractible rings] The section introducing the description of the condensed Galois category via w-contractible rings and Lurie's ultracategories must explicitly verify that the new category reproduces the objects, morphisms, and Galois actions of the Barwick-Glasman-Haine category when restricted to Dedekind domains. The non-triviality result for Spec(Z) is load-bearing on this equivalence; any mismatch would render the formula an artifact of the new presentation rather than a property of the original condensed Galois category.
- [Formula for the condensed fundamental group of Dedekind domains] In the computation of the formula for the underlying group of the condensed fundamental group of a general Dedekind domain, the derivation should include a direct reduction or comparison showing that the formula agrees with the profinite completion extracted from the original Barwick-Glasman-Haine category (rather than solely from the ultracategory description). The non-triviality claim for Spec(Z) requires an explicit example or computation confirming the group is non-trivial under the original definition.
- [Classification of schemes with initial/terminal objects] The classification of schemes with initial or terminal objects in the Galois category is used to deduce trivial condensed homotopy types. The paper should clarify how this classification interacts with the condensed structure when applied to Spec(Z) or other Dedekind domains, particularly whether the initial/terminal object property survives the extension to w-contractible rings.
minor comments (2)
- [Introduction and notation] Notation for the 'underlying group' of the condensed fundamental group should be defined more explicitly, including how it is extracted from the ultracategory or Galois category.
- [Throughout] The manuscript would benefit from additional cross-references to specific results in Barwick-Glasman-Haine and Lurie to make the extension steps easier to follow.
Simulated Author's Rebuttal
We thank the referee for their careful reading of the manuscript and for the constructive major comments. We address each point below and indicate the revisions we will make to strengthen the presentation and ensure the results are firmly grounded in the original Barwick-Glasman-Haine framework.
read point-by-point responses
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Referee: [Description of the condensed Galois category via w-contractible rings] The section introducing the description of the condensed Galois category via w-contractible rings and Lurie's ultracategories must explicitly verify that the new category reproduces the objects, morphisms, and Galois actions of the Barwick-Glasman-Haine category when restricted to Dedekind domains. The non-triviality result for Spec(Z) is load-bearing on this equivalence; any mismatch would render the formula an artifact of the new presentation rather than a property of the original condensed Galois category.
Authors: We agree that an explicit verification of the equivalence is required. In the revised manuscript we will add a dedicated subsection that constructs functors in both directions between the w-contractible ring description and the Barwick-Glasman-Haine condensed Galois category (restricted to Dedekind domains), verifies that these functors are inverse equivalences, and checks that they preserve morphisms and Galois actions. This will confirm that the non-triviality result for Spec(Z) holds with respect to the original category. revision: yes
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Referee: [Formula for the condensed fundamental group of Dedekind domains] In the computation of the formula for the underlying group of the condensed fundamental group of a general Dedekind domain, the derivation should include a direct reduction or comparison showing that the formula agrees with the profinite completion extracted from the original Barwick-Glasman-Haine category (rather than solely from the ultracategory description). The non-triviality claim for Spec(Z) requires an explicit example or computation confirming the group is non-trivial under the original definition.
Authors: We will insert a direct comparison proposition that reduces the derived formula to the profinite completion obtained from the original Barwick-Glasman-Haine category via the equivalence established in the preceding subsection. For the non-triviality on Spec(Z) we will add an explicit computation under the original definition, for instance by exhibiting a specific condensed cover arising from an arithmetic extension whose Galois action remains non-trivial after condensation. revision: yes
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Referee: [Classification of schemes with initial/terminal objects] The classification of schemes with initial or terminal objects in the Galois category is used to deduce trivial condensed homotopy types. The paper should clarify how this classification interacts with the condensed structure when applied to Spec(Z) or other Dedekind domains, particularly whether the initial/terminal object property survives the extension to w-contractible rings.
Authors: We will add a short clarifying paragraph immediately after the classification statement. It will note that the condensed homotopy type is functorially determined by the Galois category, so the existence of an initial or terminal object directly yields a trivial condensed homotopy type. Because the equivalence with the w-contractible ring description preserves categorical limits and colimits, the initial/terminal object property is invariant under the extension; consequently the classification applies unchanged to Dedekind domains such as Spec(Z), which lack such objects. revision: yes
Circularity Check
No significant circularity; new formula and non-triviality result for Spec(Z) are independent computations
full rationale
The paper extends the condensed Galois category from Barwick-Glasman-Haine using Lurie's ultracategories and a description via w-contractible rings, then classifies schemes with initial/terminal objects to deduce trivial homotopy type (referencing a prior study) and derives an explicit formula for the condensed fundamental group of Dedekind domains. The non-triviality for Spec(Z) follows from applying this formula to Z, without any reduction of the output to a fitted parameter, self-definition, or load-bearing self-citation chain. The framework is applied to standard properties of Dedekind domains and schemes, making the central claims externally falsifiable and not equivalent to the inputs by construction.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Standard properties of schemes, Dedekind domains, and Galois categories as in Barwick-Glasman-Haine and Lurie.
Lean theorems connected to this paper
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IndisputableMonolith/Foundation/AbsoluteFloorClosure.leanabsoluteFloorClosureCert unclearWe extend the study of the condensed Galois category of a scheme introduced by Barwick, Glasman and Haine... provide a description in terms of w-contractible rings... compute a formula for the (underlying group of the) condensed fundamental group of a general Dedekind domain
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IndisputableMonolith/Foundation/AlexanderDuality.leanalexander_duality_circle_linking unclearTheorem 3.38... Gal(X)(S) identifies with the category whose objects are w-contractible rings A lying above X... morphisms are given by maps of rings inducing the identity on π0
Reference graph
Works this paper leans on
-
[1]
Haine and Sebastian Wolf , year=
Magnus Carlson and Peter J. Haine and Sebastian Wolf , year=. Reconstruction of schemes from their \'. 2407.19920 , archivePrefix=
- [2]
-
[3]
Hebestreit, Fabian and Steinebrunner, Jan , TITLE =. Int. Math. Res. Not. IMRN , FJOURNAL =. 2025 , NUMBER =. doi:10.1093/imrn/rnaf021 , URL =
-
[4]
Vechtomov, E. M. , TITLE =. Uspekhi Mat. Nauk , FJOURNAL =. 1992 , NUMBER =. doi:10.1070/RM1992v047n05ABEH000961 , URL =
-
[5]
Vechtomov, E. M. , TITLE =. J. Math. Sci. , FJOURNAL =. 1996 , NUMBER =. doi:10.1007/BF02363066 , URL =
-
[6]
Vechtomov, E. M. , TITLE =. Mat. Zametki , FJOURNAL =. 1994 , NUMBER =. doi:10.1007/BF02110350 , URL =
- [7]
-
[8]
Galois Cohomology and Class Field Theory , url =
Harari, David , year =. Galois Cohomology and Class Field Theory , url =
- [9]
- [10]
-
[11]
and Prestel, Alexander , year =
Engler, Antonio J. and Prestel, Alexander , year =. Valued fields , url =
-
[12]
Algebraic number theory , address =
Neukirch, Jürgen , year =. Algebraic number theory , address =
- [13]
-
[14]
Feng, Tony , TITLE =. Compos. Math. , FJOURNAL =. 2020 , NUMBER =. doi:10.1112/s0010437x20007216 , URL =
- [15]
-
[16]
Martini, Louis and Wolf, Sebastian , TITLE =. High. Struct. , FJOURNAL =. 2024 , NUMBER =
work page 2024
-
[17]
Krull, Wolfgang and Neukirch, Jürgen , TITLE =. Math. Ann. , FJOURNAL =. 1971 , PAGES =. doi:10.1007/BF02052391 , URL =
-
[18]
Wolf, Sebastian , TITLE =. Doc. Math. , FJOURNAL =. 2022 , PAGES =
work page 2022
- [19]
- [20]
- [21]
- [22]
-
[23]
Clausen, Dustin and Jansen, Mikala Ørsnes , TITLE =. Selecta Math. (N.S.) , FJOURNAL =. 2024 , NUMBER =. doi:10.1007/s00029-023-00900-8 , URL =
-
[24]
Douady, Adrien , TITLE =. C. R. Acad. Sci. Paris , FJOURNAL =. 1964 , PAGES =
work page 1964
-
[25]
Haran, Dan and Jarden, Moshe , TITLE =. Pacific J. Math. , FJOURNAL =. 2000 , NUMBER =. doi:10.2140/pjm.2000.196.445 , URL =
-
[26]
Recent developments in the inverse
Jarden, Moshe , TITLE =. Recent developments in the inverse. 1995 , ISBN =. doi:10.1090/conm/186/02192 , URL =
-
[27]
Moerdijk, Ieke and Nuiten, Joost , TITLE =. Algebr. Geom. Topol. , FJOURNAL =. 2020 , NUMBER =. doi:10.2140/agt.2020.20.1769 , URL =
-
[28]
Animated Condensed Sets and Their Homotopy Groups , Year =
Mair, Catrin , Month =. Animated Condensed Sets and Their Homotopy Groups , Year =
-
[29]
Classifying anima of condensed -categories of points , author=. 2026 , eprint=
work page 2026
- [31]
- [32]
-
[33]
and Ramzi, Maxime and Steinebrunner, Jan , TITLE =
Haine, Peter J. and Ramzi, Maxime and Steinebrunner, Jan , TITLE =. 2022 , NOTE =
work page 2022
-
[34]
Yoneda's lemma for internal higher categories , Month =
Martini, Louis , Note =. Yoneda's lemma for internal higher categories , Month =
-
[35]
Constructible sheaves on schemes and a categorical
Hemo, Tamir and Richarz, Timo and Scholbach, Jakob , Month =. Constructible sheaves on schemes and a categorical
-
[36]
A categorical Künneth formula for constructible Weil sheaves , volume=
Hemo, Tamir and Richarz, Timo and Scholbach, Jakob , year=. A categorical Künneth formula for constructible Weil sheaves , volume=. Algebra & Number Theory , publisher=. doi:10.2140/ant.2024.18.499 , number=
-
[37]
Hemo, Tamir and Richarz, Timo and Scholbach, Jakob , TITLE =. Adv. Math. , FJOURNAL =. 2023 , PAGES =. doi:10.1016/j.aim.2023.109179 , URL =
-
[38]
Cohomology of number fields , SERIES =
Neukirch, J\". Cohomology of number fields , SERIES =. 2008 , PAGES =. doi:10.1007/978-3-540-37889-1 , URL =
-
[39]
Scanlon, Thomas , Note =. Infinite stable fields are. 1999 , Month =
work page 1999
-
[40]
Kaplan, Itay and Scanlon, Thomas and Wagner, Frank O. , TITLE =. Israel J. Math. , FJOURNAL =. 2011 , PAGES =. doi:10.1007/s11856-011-0104-7 , URL =
-
[41]
Zargar, Masoud , TITLE =. Adv. Math. , FJOURNAL =. 2019 , PAGES =. doi:10.1016/j.aim.2019.106744 , URL =
-
[42]
Geometrization of the local Langlands correspondence , Year =
Fargues, Laurent and Scholze, Peter , Month =. Geometrization of the local Langlands correspondence , Year =
-
[43]
The tame site of a scheme , JOURNAL =
H\". The tame site of a scheme , JOURNAL =. 2021 , NUMBER =. doi:10.1007/s00222-020-00993-4 , URL =
- [44]
-
[45]
Schmidt, Alexander , TITLE =. Compositio Math. , FJOURNAL =. 1996 , NUMBER =
work page 1996
-
[46]
Temkin, Michael , TITLE =. Ann. of Math. (2) , FJOURNAL =. 2017 , NUMBER =. doi:10.4007/annals.2017.186.1.3 , URL =
-
[47]
On Gabber's refined uniformization , Year =
Illusie, Luc , Note =. On Gabber's refined uniformization , Year =
-
[48]
Hoyois, Marc and Kelly, Shane and Østvær, Paul Arne , TITLE =. J. Eur. Math. Soc. (JEMS) , FJOURNAL =. 2017 , NUMBER =. doi:10.4171/JEMS/754 , URL =
-
[49]
Elmanto, Elden and Hoyois, Marc and Iwasa, Ryomei and Kelly, Shane , TITLE =. J. Reine Angew. Math. , FJOURNAL =. 2021 , PAGES =. doi:10.1515/crelle-2021-0040 , URL =
-
[50]
Elmanto, Elden and Hoyois, Marc and Iwasa, Ryomei and Kelly, Shane , TITLE =. Math. Ann. , FJOURNAL =. 2021 , NUMBER =. doi:10.1007/s00208-020-02083-5 , URL =
-
[51]
Bhatt, Bhargav and Mathew, Akhil , TITLE =. Duke Math. J. , FJOURNAL =. 2021 , NUMBER =. doi:10.1215/00127094-2020-0088 , URL =
-
[52]
Anel, Mathieu and Biedermann, Georg and Finster, Eric and Joyal, André , TITLE =. J. Topol. , FJOURNAL =. 2020 , NUMBER =. doi:10.1112/topo.12163 , URL =
-
[53]
Orgogozo, Fabrice , TITLE =. Bull. Soc. Math. France , FJOURNAL =. 2003 , NUMBER =. doi:10.24033/bsmf.2438 , URL =
-
[54]
Invariance of the fundamental group under base change between algebraically closed fields , Year =
Landesman, Aaron , Month =. Invariance of the fundamental group under base change between algebraically closed fields , Year =
-
[55]
Lara, Marcin , TITLE =. Int. Math. Res. Not. IMRN , FJOURNAL =. 2022 , NUMBER =. doi:10.1093/imrn/rnab101 , URL =
-
[56]
Algebra Number Theory , FJOURNAL =
Lara, Marcin , TITLE =. Algebra Number Theory , FJOURNAL =. 2024 , NUMBER =. doi:10.2140/ant.2024.18.631 , URL =
- [57]
-
[58]
and Holzschuh, Tim and Wolf, Sebastian , TITLE =
Haine, Peter J. and Holzschuh, Tim and Wolf, Sebastian , TITLE =. J. Topol. , FJOURNAL =. 2024 , NUMBER =. doi:10.1112/topo.70009 , URL =
-
[59]
and Holzschuh, Tim and Wolf, Sebastian , TITLE =
Haine, Peter J. and Holzschuh, Tim and Wolf, Sebastian , TITLE =. Int. Math. Res. Not. IMRN , FJOURNAL =. 2024 , NUMBER =. doi:10.1093/imrn/rnad018 , URL =
-
[60]
Lu, Qing and Zheng, Weizhe , TITLE =. Duke Math. J. , FJOURNAL =. 2019 , NUMBER =. doi:10.1215/00127094-2019-0057 , URL =
-
[61]
Carchedi, David and Scherotzke, Sarah and Sibilla, Nicolò and Talpo, Mattia , TITLE =. 2019 , NOTE =
work page 2019
-
[62]
Carchedi, David and Scherotzke, Sarah and Sibilla, Nicol\`o and Talpo, Mattia , TITLE =. Geom. Topol. , FJOURNAL =. 2017 , NUMBER =. doi:10.2140/gt.2017.21.3093 , URL =
-
[63]
Schlank, Tomer M. and Skorobogatov, Alexei N. , TITLE =. Torsors, étale homotopy and applications to rational points , SERIES =. 2013 , MRCLASS =
work page 2013
- [64]
-
[65]
Devalapurkar, Sanath and Haine, Peter , TITLE =. Doc. Math. , FJOURNAL =. 2021 , PAGES =
work page 2021
- [66]
-
[67]
Friedlander, Eric M. , TITLE =. Manuscripta Math. , FJOURNAL =. 1973 , PAGES =. doi:10.1007/BF01332767 , URL =
- [68]
-
[69]
Quick, Gereon , TITLE =. J. Pure Appl. Algebra , FJOURNAL =. 2011 , NUMBER =. doi:10.1016/j.jpaa.2010.07.008 , URL =
-
[70]
Cox, David A. , TITLE =. Proc. Amer. Math. Soc. , FJOURNAL =. 1979 , NUMBER =. doi:10.2307/2042908 , URL =
-
[71]
Gepner, David and Kock, Joachim , TITLE =. Forum Math. , FJOURNAL =. 2017 , NUMBER =. doi:10.1515/forum-2015-0228 , URL =
-
[72]
Neeman, Amnon , TITLE =. Doc. Math. , FJOURNAL =. 2001 , PAGES =
work page 2001
-
[73]
Hesselholt, Lars and Pstrągowski, Piotr , TITLE =. Peking Math. J. , FJOURNAL =. 2025 , NUMBER =. doi:10.1007/s42543-023-00072-6 , URL =
- [74]
-
[75]
Aoki, Ko , TITLE =. Math. Z. , FJOURNAL =. 2023 , NUMBER =. doi:10.1007/s00209-023-03210-z , URL =
-
[76]
and Porta, Mauro and Teyssier, Jean-Baptiste , TITLE =
Haine, Peter J. and Porta, Mauro and Teyssier, Jean-Baptiste , TITLE =. Homology Homotopy Appl. , FJOURNAL =. 2023 , NUMBER =. doi:10.4310/hha.2023.v25.n2.a6 , URL =
-
[77]
Dyckhoff, Roy , TITLE =. Categorical topology (. 1976 , MRCLASS =
work page 1976
-
[78]
Synthetic spectra and the cellular motivic category , Year =
Pstrągowski, Piotr , Month =. Synthetic spectra and the cellular motivic category , Year =
-
[79]
Six functor formalism for sheaves with non-presentable coefficients , Year =
Volpe, Marco , Month =. Six functor formalism for sheaves with non-presentable coefficients , Year =
-
[80]
Hoyois, Marc , Month =
- [81]
discussion (0)
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