The unreasonable power of the lifting property in elementary mathematics. A draft of a research proposal. As a text file (slightly outdated) or a tex file.
Expressing the statement of the Feit-Thompson theorem with diagrams in the category of finite groups. same in djvu,
Elementary general topology as diagram chasing calculations with finite categories. A draft of a research proposal. same in djvu,
Separation axioms as Quillen lifting properties, a modified wikipedia page
An example of a lifting property, slides
Point set topology as diagram chasing computations. Lifting properties as instances of negation. same in djvu, as published in De Morgan Gazette. 8p. An updated version, 14pp.
Point-set topology as diagram chasing computations. same in djvu, 21 page. A draft of a research proposal.
A decidable equational fragment of category theory without automorphisms. 6 pages, joint with Alexandre Luzgarev and Vladimir Sosnilo. A preliminary draft (a beta-version; read at your own risk!). The first public version (pre-July 2014)
Exercises de style: A homotopy theory for set theory. Part I and II., joint with Assaf Hasson, 51 page, a shortened exposition of the two preprints below
Exercises de style: A homotopy theory for set theory. Part I., same in djvu, joint with Assaf Hasson, 36 pages, a paper explaining the main construction but not set theoretic applications.
Exercises de style: A homotopy theory for set theory. Part II., same in djvu, joint with Assaf Hasson, 36 pages, a paper about set theoretic applications
The univalence axiom for posetal model categories. A shortened version. joint with Assaf Hasson and Itay Kaplan, 12 pages, a note where we observe that the set-theoretic model category constructed in "Exercises de style" delivers an example of the Univalence Axiom, albeit in a rather trivial way.
My DPhil thesis Model Theory of the Universal Covering Spaces of Complex Algebraic Varieties. Please note parts of it are superseded by later work of Martin Bays, esp. Categoricity results for exponential maps of 1-dimensional algebraic groups & Schanuel Conjectures for Powers and the CIT. Please note there is an innaccuracy in the definition of the topology in section II.1.2, which is corrected in the preprint Covers of Abelian varieties as analytic Zariski structures, and an error in chapter IV which is corrected in the paper A remark on transitivity of Galois action on the set of uniquely divisible abelian extensions of E(bar Q) by Z2.
The unreasonable power of the lifting property in elementary mathematics. We illustrate the generative power of the lifting property as a means of defining natural elementary mathematical concepts by giving a number of examples in various categories, in particular showing that many standard elementary notions of abstract topology can be defined by applying the lifting property to simple morphisms of finite topological spaces. We include some speculations on the wider significance of this. A draft. As a text file (more convenient for some readers).
Expressing the statement of the Feit-Thompson theorem with diagrams in the category of finite groups. same in djvu, We reformulate the statement of the Feit-Thompson theorem in terms of diagrams in the category of finite groups, namely iterations of the Quillen lifting property with respect to particular morphisms.
Elementary general topology as diagram chasing calculations with finite categories. same in djvu, We observe that elementary general topology arguments can be seen as diagram chasing computations with finite categories, via a straightforward, naive translation which often involves the Quillen lifting property playing the role of negation.
This paper is a draft of a research proposal: we argue it is worthwhile to to try to see whether these observations lead to another axiomatisation of topology and a proof system amenable to automatic theorem proving. Help in proofreading much appreciated.
An example of a lifting property, slides. We explain how an example of a proof in (Ganesalingam, Gowers, {\em A fully automatic problem solver with human-style output} is a sequence of applications of a single diagram chasing rule, the lifting property. Their example is: a closed subset of a complete metric space is complete.
We observe that some natural mathematical definitions are lifting properties
relative to simplest counterexamples, namely the definitions of surjectivity and injectivity of maps,
as well as of being connected, separation axioms T
We also offer a couple of brief speculations on cognitive and AI aspects of this observation, particularly that in point-set topology some arguments read as diagram chasing computations with finite preorders.
An updated version with new examples in group theory--abelian, perfect, p-groups, groups of order prime to p, soluble (in finite groups), and Feit-Thompson theorem reformulated in terms of lifting properties.
We give several examples of properties in point-set topology, such as being Hausdorff or that equalizier {x:f(x)=g(x)} is being closed for maps to a Hausdorff space, that translate to diagram chasing rules, and where the lifting property is a "category theory negation". We suggest this observation can be implemented in a problem solver of a kind suggested by M. Ganesalingam and T. Gowers. This is a preliminary publication; perhaps a little more like a research proposal that a proper paper.
A decidable equational fragment of category theory without automorphisms. 6 pages, joint with Alexandre Luzgarev and Vladimir Sosnilo. A preliminary draft (a beta-version; read at your own risk!)
Exercises de style: A homotopy theory for set theory. Part I and II., joint with Assaf Hasson, 51 page, a shortened exposition of the two preprints below
Exercises de style: A homotopy theory for set theory. Part I., same in djvu, joint with Assaf Hasson, 36 pages, a paper explaining the main construction but not set theoretic applications.
Exercises de style: A homotopy theory for set theory. Part II., same in djvu, joint with Assaf Hasson, 36 pages, a paper about set theoretic applications
The univalence axiom for posetal model categories. A shortened version. joint with Assaf Hasson and Itay Kaplan, 12 pages, a note where we observe that the set-theoretic model category constructed in "Exercises de style" delivers an example of the Univalence Axiom, albeit in a rather trivial way.
A little place to discuss QtNaamen (typos, corrections, questions...)
A description/summary of the preprints below:We construct a model category and use it to introduce homotopy-theoretic intuitions to set theory. Our main observation is that the homotopy invariant version of cardinality is the covering number of Shelah's PCF theory, and that other combinatorial objects, such as Shelah's revised power function - the cardinal function featuring in Shelah's revised GCH theorem - can be obtained using similar tools. We include a small "dictionary" for set theory in the model category QtNaamen, hoping it will help in finding more meaningful homotopy-theoretic intuitions in set theory.
- Yuri Manin gives a nice description of some background relevant to the works above:
3.4. Quillen’s homotopical algebra and univalent foundations project. In his influential book [Qu] Quillen developed the idea that the natural language for homotopy theory should appeal not to the initial intuition of continuous deformation itself, but rather to a codified list of properties of category of topological spaces stressing those that are relevant for studying homotopy.
Quillen defined a closed model category as a category endowed with three special classes of morphisms: fibrations, cofibrations, and weak equivalences. The list of axioms to which these three classes of morphisms must satisfy is not long but structurally quite sophisticated. They can be easily defined in the category of topological spaces using homotopy intuition but remarkably admit translation into many other situations. An interesting new preprint [GaHa] even suggests the definition of these classes in appropriate categories of discrete sets, contributing new insights to old Cantorian problems of the scale of infinities.
Closed model categories become in particular a language of preference for many contexts in which objects of study are quotients of “large” objects by “large” equivalence relations, such as homotopy.
It is thus only natural that the most recent Foundation/Superstructure, Vo- evodsky’s Univalent Foundations Project (cf. [Vo] and [Aw]) is based on direct axiomatization of the world of homotopy types.