On Numbers, Germs, and Transseries
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An Very Brief Overview of Surreal Numbers for Gandalf MM 2014
An very brief overview of Surreal Numbers for Gandalf MM 2014 Steven Charlton 1 History and Introduction Surreal numbers were created by John Horton Conway (of Game of Life fame), as a greatly simplified construction of an earlier object (Alling’s ordered field associated to the class of all ordinals, as constructed via modified Hahn series). The name surreal numbers was coined by Donald Knuth (of TEX and the Art of Computer Programming fame) in his novel ‘Surreal Numbers’ [2], where the idea was first presented. Surreal numbers form an ordered Field (Field with a capital F since surreal numbers aren’t a set but a class), and are in some sense the largest possible ordered Field. All other ordered fields, rationals, reals, rational functions, Levi-Civita field, Laurent series, superreals, hyperreals, . , can be found as subfields of the surreals. The definition/construction of surreal numbers leads to a system where we can talk about and deal with infinite and infinitesimal numbers as naturally and consistently as any ‘ordinary’ number. In fact it let’s can deal with even more ‘wonderful’ expressions 1 √ 1 ∞ − 1, ∞, ∞, ,... 2 ∞ in exactly the same way1. One large area where surreal numbers (or a slight generalisation of them) finds application is in the study and analysis of combinatorial games, and game theory. Conway discusses this in detail in his book ‘On Numbers and Games’ [1]. 2 Basic Definitions All surreal numbers are constructed iteratively out of two basic definitions. This is an wonderful illustration on how a huge amount of structure can arise from very simple origins. -
Formal Power Series - Wikipedia, the Free Encyclopedia
Formal power series - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Formal_power_series Formal power series From Wikipedia, the free encyclopedia In mathematics, formal power series are a generalization of polynomials as formal objects, where the number of terms is allowed to be infinite; this implies giving up the possibility to substitute arbitrary values for indeterminates. This perspective contrasts with that of power series, whose variables designate numerical values, and which series therefore only have a definite value if convergence can be established. Formal power series are often used merely to represent the whole collection of their coefficients. In combinatorics, they provide representations of numerical sequences and of multisets, and for instance allow giving concise expressions for recursively defined sequences regardless of whether the recursion can be explicitly solved; this is known as the method of generating functions. Contents 1 Introduction 2 The ring of formal power series 2.1 Definition of the formal power series ring 2.1.1 Ring structure 2.1.2 Topological structure 2.1.3 Alternative topologies 2.2 Universal property 3 Operations on formal power series 3.1 Multiplying series 3.2 Power series raised to powers 3.3 Inverting series 3.4 Dividing series 3.5 Extracting coefficients 3.6 Composition of series 3.6.1 Example 3.7 Composition inverse 3.8 Formal differentiation of series 4 Properties 4.1 Algebraic properties of the formal power series ring 4.2 Topological properties of the formal power series -
An Introduction to Conway's Games and Numbers
AN INTRODUCTION TO CONWAY’S GAMES AND NUMBERS DIERK SCHLEICHER AND MICHAEL STOLL 1. Combinatorial Game Theory Combinatorial Game Theory is a fascinating and rich theory, based on a simple and intuitive recursive definition of games, which yields a very rich algebraic struc- ture: games can be added and subtracted in a very natural way, forming an abelian GROUP (§ 2). There is a distinguished sub-GROUP of games called numbers which can also be multiplied and which form a FIELD (§ 3): this field contains both the real numbers (§ 3.2) and the ordinal numbers (§ 4) (in fact, Conway’s definition gen- eralizes both Dedekind sections and von Neumann’s definition of ordinal numbers). All Conway numbers can be interpreted as games which can actually be played in a natural way; in some sense, if a game is identified as a number, then it is under- stood well enough so that it would be boring to actually play it (§ 5). Conway’s theory is deeply satisfying from a theoretical point of view, and at the same time it has useful applications to specific games such as Go [Go]. There is a beautiful microcosmos of numbers and games which are infinitesimally close to zero (§ 6), and the theory contains the classical and complete Sprague-Grundy theory on impartial games (§ 7). The theory was founded by John H. Conway in the 1970’s. Classical references are the wonderful books On Numbers and Games [ONAG] by Conway, and Win- ning Ways by Berlekamp, Conway and Guy [WW]; they have recently appeared in their second editions. -
On Numbers, Germs, and Transseries
On Numbers, Germs, and Transseries Matthias Aschenbrenner, Lou van den Dries, Joris van der Hoeven Abstract Germs of real-valued functions, surreal numbers, and transseries are three ways to enrich the real continuum by infinitesimal and infinite quantities. Each of these comes with naturally interacting notions of ordering and deriva- tive. The category of H-fields provides a common framework for the relevant algebraic structures. We give an exposition of our results on the model theory of H-fields, and we report on recent progress in unifying germs, surreal num- bers, and transseries from the point of view of asymptotic differential algebra. Contemporaneous with Cantor's work in the 1870s but less well-known, P. du Bois- Reymond [10]{[15] had original ideas concerning non-Cantorian infinitely large and small quantities [34]. He developed a \calculus of infinities” to deal with the growth rates of functions of one real variable, representing their \potential infinity" by an \actual infinite” quantity. The reciprocal of a function tending to infinity is one which tends to zero, hence represents an \actual infinitesimal”. These ideas were unwelcome to Cantor [39] and misunderstood by him, but were made rigorous by F. Hausdorff [46]{[48] and G. H. Hardy [42]{[45]. Hausdorff firmly grounded du Bois-Reymond's \orders of infinity" in Cantor's set-theoretic universe [38], while Hardy focused on their differential aspects and introduced the logarithmico-exponential functions (short: LE-functions). This led to the concept of a Hardy field (Bourbaki [22]), developed further mainly by Rosenlicht [63]{[67] and Boshernitzan [18]{[21]. For the role of Hardy fields in o-minimality see [61]. -
Local Topological Algebraicity of Analytic Function Germs Marcin Bilski, Adam Parusinski, Guillaume Rond
Local topological algebraicity of analytic function germs Marcin Bilski, Adam Parusinski, Guillaume Rond To cite this version: Marcin Bilski, Adam Parusinski, Guillaume Rond. Local topological algebraicity of analytic function germs. Journal of Algebraic Geometry, American Mathematical Society, 2017, 26 (1), pp.177 - 197. 10.1090/jag/667. hal-01255235 HAL Id: hal-01255235 https://hal.archives-ouvertes.fr/hal-01255235 Submitted on 13 Jan 2016 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. LOCAL TOPOLOGICAL ALGEBRAICITY OF ANALYTIC FUNCTION GERMS MARCIN BILSKI, ADAM PARUSINSKI,´ AND GUILLAUME ROND Abstract. T. Mostowski showed that every (real or complex) germ of an analytic set is homeomorphic to the germ of an algebraic set. In this paper we show that every (real or com- plex) analytic function germ, defined on a possibly singular analytic space, is topologically equivalent to a polynomial function germ defined on an affine algebraic variety. 1. Introduction and statement of results The problem of approximation of analytic objects (sets or mappings) by algebraic ones has attracted many mathematicians, see e.g. [2] and the bibliography therein. Nevertheless there are very few positive results if one requires that the approximation gives a homeomorphism between the approximated object and the approximating one. -
On Numbers, Germs, and Transseries
On Numbers, Germs, and Transseries Matthias Aschenbrenner, Lou van den Dries, Joris van der Hoeven Abstract Germs of real-valued functions, surreal numbers, and transseries are three ways to enrich the real continuum by infinitesimal and infinite quantities. Each of these comes with naturally interacting notions of ordering and deriva- tive. The category of H-fields provides a common framework for the relevant algebraic structures. We give an exposition of our results on the model theory of H-fields, and we report on recent progress in unifying germs, surreal num- bers, and transseries from the point of view of asymptotic differential algebra. Contemporaneous with Cantor's work in the 1870s but less well-known, P. du Bois- Reymond [10]{[15] had original ideas concerning non-Cantorian infinitely large and small quantities [34]. He developed a \calculus of infinities” to deal with the growth rates of functions of one real variable, representing their \potential infinity" by an \actual infinite” quantity. The reciprocal of a function tending to infinity is one which tends to zero, hence represents an \actual infinitesimal”. These ideas were unwelcome to Cantor [39] and misunderstood by him, but were made rigorous by F. Hausdorff [46]{[48] and G. H. Hardy [42]{[45]. Hausdorff firmly grounded du Bois-Reymond's \orders of infinity" in Cantor's set-theoretic universe [38], while Hardy focused on their differential aspects and introduced the logarithmico-exponential functions (short: LE-functions). This led to the concept of a Hardy field (Bourbaki [22]), developed further mainly by Rosenlicht [63]{[67] and Boshernitzan [18]{[21]. For the role of Hardy fields in o-minimality see [61]. -
SHEAF THEORY 1. Presheaves Definition 1.1. a Presheaf on A
SHEAF THEORY 1. Presheaves Definition 1.1. A presheaf on a space X (any top. space) is a contravariant functor from open sets on X to a category (usually Ab= category of abelian groups). That is, given U open ⊆ X, you have an abelian group A (U), and if V ⊆ U, then you have a restriction map rV,U : A (U) → A (V ). Then rU,U = 1, rW,V rV,U = rW,U etc. Example 1.2. Let A (U) = G, a fixed abelian group ∀U, rU,V = 1 (constant presheaf) Example 1.3. Let A (U) = G, a fixed abelian group ∀U, rU,V = 0 (Texas A&M presheaf) Example 1.4. Let A (X) = G, A (U) = 0 ∀proper U ⊆ X (TCC presheaf) 0 if x∈ / U Example 1.5. Skyscraper presheaf: x ∈ X; A (U) = G if x ∈ U Example 1.6. X = M, A (U) = {real analytic fcns on U} Example 1.7. adapt above using words like continuous, holomorphic, polynomial, differen- tial forms, kth cohomology group Hk (U), ∞ ∞ 2 Example 1.8. or Hk (U) (closed support homology). For example, Hk (open disk in R ) = Z k = 2 0 otherwise restriction maps: cut things off ∗ ∞ Note: Poincare duality for closed support: H (M) = Hn−∗ (M)(M possibly noncompact) ∗ c Poincare duality for compact support: Hc (M) = Hn−∗ (M) ∞ Example 1.9. Orientation presheaf: on an n-manifold, Hn (U) 2. Sheaves Definition 2.1. A sheaf A is a space together with a projection π : A → X such that −1 (1) Ax := π (x) is an abelian group (or could generalize to other categories) ∀x ∈ X (stalk at x) (2) π is a local homeomorphism (⇒ π−1 (x) is discrete) (3) group operations are continuous, ie {(a, b) ∈ A × A | π (a) = π (b)} → A given by (a, b) 7→ ab−1 is continuous. -
Blue-Red Hackenbush
Basic rules Two players: Blue and Red. Perfect information. Players move alternately. First player unable to move loses. The game must terminate. Mathematical Games – p. 1 Outcomes (assuming perfect play) Blue wins (whoever moves first): G > 0 Red wins (whoever moves first): G < 0 Mover loses: G = 0 Mover wins: G0 Mathematical Games – p. 2 Two elegant classes of games number game: always disadvantageous to move (so never G0) impartial game: same moves always available to each player Mathematical Games – p. 3 Blue-Red Hackenbush ground prototypical number game: Blue-Red Hackenbush: A player removes one edge of his or her color. Any edges not connected to the ground are also removed. First person unable to move loses. Mathematical Games – p. 4 An example Mathematical Games – p. 5 A Hackenbush sum Let G be a Blue-Red Hackenbush position (or any game). Recall: Blue wins: G > 0 Red wins: G < 0 Mover loses: G = 0 G H G + H Mathematical Games – p. 6 A Hackenbush value value (to Blue): 3 1 3 −2 −3 sum: 2 (Blue is two moves ahead), G> 0 3 2 −2 −2 −1 sum: 0 (mover loses), G= 0 Mathematical Games – p. 7 1/2 value = ? G clearly >0: Blue wins mover loses! x + x - 1 = 0, so x = 1/2 Blue is 1/2 move ahead in G. Mathematical Games – p. 8 Another position What about ? Mathematical Games – p. 9 Another position What about ? Clearly G< 0. Mathematical Games – p. 9 −13/8 8x + 13 = 0 (mover loses!) x = -13/8 Mathematical Games – p. -
Combinatorial Game Theory
Combinatorial Game Theory Aaron N. Siegel Graduate Studies MR1EXLIQEXMGW Volume 146 %QIVMGER1EXLIQEXMGEP7SGMIX] Combinatorial Game Theory https://doi.org/10.1090//gsm/146 Combinatorial Game Theory Aaron N. Siegel Graduate Studies in Mathematics Volume 146 American Mathematical Society Providence, Rhode Island EDITORIAL COMMITTEE David Cox (Chair) Daniel S. Freed Rafe Mazzeo Gigliola Staffilani 2010 Mathematics Subject Classification. Primary 91A46. For additional information and updates on this book, visit www.ams.org/bookpages/gsm-146 Library of Congress Cataloging-in-Publication Data Siegel, Aaron N., 1977– Combinatorial game theory / Aaron N. Siegel. pages cm. — (Graduate studies in mathematics ; volume 146) Includes bibliographical references and index. ISBN 978-0-8218-5190-6 (alk. paper) 1. Game theory. 2. Combinatorial analysis. I. Title. QA269.S5735 2013 519.3—dc23 2012043675 Copying and reprinting. Individual readers of this publication, and nonprofit libraries acting for them, are permitted to make fair use of the material, such as to copy a chapter for use in teaching or research. Permission is granted to quote brief passages from this publication in reviews, provided the customary acknowledgment of the source is given. Republication, systematic copying, or multiple reproduction of any material in this publication is permitted only under license from the American Mathematical Society. Requests for such permission should be addressed to the Acquisitions Department, American Mathematical Society, 201 Charles Street, Providence, Rhode Island 02904-2294 USA. Requests can also be made by e-mail to [email protected]. c 2013 by the American Mathematical Society. All rights reserved. The American Mathematical Society retains all rights except those granted to the United States Government. -
Math 396. Derivations and Vector Fields the Aim of These Notes Is To
Math 396. Derivations and vector fields The aim of these notes is to work out the precise correspondence between C1 vector fields and derivations on C1 functions over open sets in a C1 premanifold with corners X. Throughout what follows, all vector fields, functions, and premanifolds are understood to be of class C1, which we may abbreviate by the word \smooth". 1. Main result Let (X; O) be a smooth premanifold with corners. For any open set U X, we let VecX (U) ⊆ be the set of smooth vector fields ~v on U. Let DerX (U) be the set of R-linear derivations D of , by which we mean a collection R-linear derivations D : (U ) (U ) for all open U U O U U 0 O 0 O 0 0 satisfyingj the compatibility condition with respect to restrictions: if!U U is an inclusion⊆ of 00 ⊆ 0 opens in U then for all f O(U ) we have DU (f) U = DU (f U ) in O(U ). 2 0 0 j 00 00 j 00 00 For any ~v VecX (U) we define D~v to be the collection of maps 2 D~v;U : O(U 0) h : U 0 R 0 ! f ! g given by D (f): u ~v(u )(f) R for open U U. Roughly speaking, D maps a smooth ~v;U 0 0 0 0 ~v;U 0 function on U to the function7! whose2 value at each⊆ point u U is the directional derivative of f 0 0 2 0 in the direction ~v(u ) Tu (U ) = Tu (X) at u . -
NOTES in COMMUTATIVE ALGEBRA: PART 1 1. Results/Definitions Of
NOTES IN COMMUTATIVE ALGEBRA: PART 1 KELLER VANDEBOGERT 1. Results/Definitions of Ring Theory It is in this section that a collection of standard results and definitions in commutative ring theory will be presented. For the rest of this paper, any ring R will be assumed commutative with identity. We shall also use "=" and "∼=" (isomorphism) interchangeably, where the context should make the meaning clear. 1.1. The Basics. Definition 1.1. A maximal ideal is any proper ideal that is not con- tained in any strictly larger proper ideal. The set of maximal ideals of a ring R is denoted m-Spec(R). Definition 1.2. A prime ideal p is such that for any a, b 2 R, ab 2 p implies that a or b 2 p. The set of prime ideals of R is denoted Spec(R). p Definition 1.3. The radical of an ideal I, denoted I, is the set of a 2 R such that an 2 I for some positive integer n. Definition 1.4. A primary ideal p is an ideal such that if ab 2 p and a2 = p, then bn 2 p for some positive integer n. In particular, any maximal ideal is prime, and the radical of a pri- mary ideal is prime. Date: September 3, 2017. 1 2 KELLER VANDEBOGERT Definition 1.5. The notation (R; m; k) shall denote the local ring R which has unique maximal ideal m and residue field k := R=m. Example 1.6. Consider the set of smooth functions on a manifold M. -
Interview with John Horton Conway
Interview with John Horton Conway Dierk Schleicher his is an edited version of an interview with John Horton Conway conducted in July 2011 at the first International Math- ematical Summer School for Students at Jacobs University, Bremen, Germany, Tand slightly extended afterwards. The interviewer, Dierk Schleicher, professor of mathematics at Jacobs University, served on the organizing com- mittee and the scientific committee for the summer school. The second summer school took place in August 2012 at the École Normale Supérieure de Lyon, France, and the next one is planned for July 2013, again at Jacobs University. Further information about the summer school is available at http://www.math.jacobs-university.de/ summerschool. John Horton Conway in August 2012 lecturing John H. Conway is one of the preeminent the- on FRACTRAN at Jacobs University Bremen. orists in the study of finite groups and one of the world’s foremost knot theorists. He has written or co-written more than ten books and more than one- received the Pólya Prize of the London Mathemati- hundred thirty journal articles on a wide variety cal Society and the Frederic Esser Nemmers Prize of mathematical subjects. He has done important in Mathematics of Northwestern University. work in number theory, game theory, coding the- Schleicher: John Conway, welcome to the Interna- ory, tiling, and the creation of new number systems, tional Mathematical Summer School for Students including the “surreal numbers”. He is also widely here at Jacobs University in Bremen. Why did you known as the inventor of the “Game of Life”, a com- accept the invitation to participate? puter simulation of simple cellular “life” governed Conway: I like teaching, and I like talking to young by simple rules that give rise to complex behavior.