What is Topology: Definition and 807 Discussions

In mathematics, topology (from the Greek words τόπος, 'place, location', and λόγος, 'study') is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing holes, opening holes, tearing, gluing, or passing through itself.
A topological space is a set endowed with a structure, called a topology, which allows defining continuous deformation of subspaces, and, more generally, all kinds of continuity. Euclidean spaces, and, more generally, metric spaces are examples of a topological space, as any distance or metric defines a topology. The deformations that are considered in topology are homeomorphisms and homotopies. A property that is invariant under such deformations is a topological property. Basic examples of topological properties are: the dimension, which allows distinguishing between a line and a surface; compactness, which allows distinguishing between a line and a circle; connectedness, which allows distinguishing a circle from two non-intersecting circles.
The ideas underlying topology go back to Gottfried Leibniz, who in the 17th century envisioned the geometria situs and analysis situs. Leonhard Euler's Seven Bridges of Königsberg problem and polyhedron formula are arguably the field's first theorems. The term topology was introduced by Johann Benedict Listing in the 19th century, although it was not until the first decades of the 20th century that the idea of a topological space was developed.

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  1. E

    Point set topology, hoemomorphism related questiosns

    Hello I am having difficulties in solving the following two questions. 1) For the first question, the author of the text states that if f:[a,b]-->R is a map, then I am f is a closed, bounded interval. Question: Let X be subset of R, and X is the union of the open intervals (3n, 3n+1) and the...
  2. C

    Digital Line Topology: Show Odd Integers are Dense in \mathbb{Z}

    Homework Statement Show that the set of odd integers is dense in the digital line topology on \mathbb{Z} The Attempt at a Solution if m in Z is odd then it gets mapped to the set {m}=> open . So is the digital line topology just the integers. If I was given any 2 integers I could...
  3. H

    Prove that the following is a Topology. I really just want to clean it up.

    Homework Statement Prove that T1={U subset of X: X\U is finite or is all of X} is a topology. Homework Equations DeMorgan's Laws will be useful. Empty set is defined as finite, and X is an arbitrary infinite set. The Attempt at a Solution 1) X/X = empty set, finite. Thus X is in T1...
  4. C

    Is the Particular Point Topology Compact?

    Homework Statement Let X be a set and p is in X, show the collection T, consisting of the empty set and all the subsets of X containing p is a topology on X. Homework Equations? A topology T on X is a collection of subsets of X. i) X is open ii) the intersection of finitely...
  5. A

    Topology, functional analysis, and group theory

    What is the relationship between topology, functional analysis, and group theory? All three seem to overlap, and I can't quite see how to distinguish them / what they're each for.
  6. P

    Topology (showing set is not open)

    Homework Statement Show [0,1] is not open in ℝ Homework Equations [0,1] is open if and only if ℝ\[0,1] is closed. The Attempt at a Solution ℝ\[0,1] = (-∞,0) U (1,∞), this set is open. Despite the if and only if statement this is enough to say that [0,1] is not open in ℝ. Is this correct?
  7. B

    Basic Topology Proof: y in E Closure if E is Closed

    Homework Statement Let E be a nonempty set of real numbers which is bounded above. Let y=sup E. Then y \in E closure. Hence y \in E if E is closed.Homework Equations E closure = E' \cup E where E' is the set of all limit points of E. The Attempt at a Solution By the definition of closure, y...
  8. F

    Homeomorphisms with the discrete topology

    Surely sets with the same cardinality are homeomorphic if we assign both of them the discrete topology. What's preventing us from doing that? For example, (0,1) and (2,3) \cup (4,5) have the same cardinality. With the natural subspace topology they are not homeomorphic - as one is connected...
  9. S

    Subspace Topology of a Straight Line

    1. Hello, I'm reading through Munkres and I was doing this problem. 16.8) If L is a straight line in the plane, describe the topology L inherits as a subspace of ℝl × ℝ and as a subspace of ℝl × ℝl (where ℝl is the lower limit topology). Homework Equations The Attempt at a Solution I've...
  10. micromass

    Study groups for calculus and topology

    Hello, Some people on PF are currently self-studying calculus and topology. So we thought we might make a post here so that interested people could join us. We are doing the following books: Book of Proof by Hammack (freely available on http://www.people.vcu.edu/~rhammack/BookOfProof/)...
  11. P

    Taking Topology, Real Analysis and Abstract Algebra concurrently a good idea?

    Hello all, In the Fall I am planning on taking Real Analysis, Abstract Algebra and doing an independent study in something(my professor has yet to get back to me on what he is willing to do it in). My question is would it be too much of a workload to try and do another independent study in...
  12. Hercuflea

    Preparing for General Topology

    Hey everybody, I just wanted to ask a general question about Topology. I am planning on taking a General Topology course in Spring 2013 and first of all I don't know what it is. I am finishing up Differential Equations 1 right now with an A. By the spring I will have taken linear algebra 2...
  13. K

    Point Set Topology: Why A={1/n:n is Counting Number} is Not a Closed Set?

    Why is it that the set A={1/n:n is counting number} is not a closed set? We see that no matter how small our ε is, ε-neighborhood will always contain a point not in A (one reason is that Q* is dense in ℝ), thus, all the elements in A is boundary point, and we know that by definition, if...
  14. M

    What are the best intro books for topology?

    I'm sure this has already been a thread but I'm currently taking my first analysis course and I was wondering (because the tiny bit I've been introduced to so far is so interesting) what the best intro books to topology would be. Thanks!
  15. K

    3D pipe unwrap to 2D topology

    Hi, I am not very strong in maths, so sorry if these sounds simple. If I have a 3D geometry of a pipe which has its surface defined by triangles (such as that in Computational Fluid Dynamics or Finite Element Analysis) and I have the coordinate points for all the triangles, how can I...
  16. Math Amateur

    Algebraic Topology - Retractions and Homomorpisms Induced by Inclusions

    I am reading Munkres book on Topology, Part II - Algegraic Topology Chapter 9 on the Fundamental Group. On page 348 Munkres gives the following Lemma concerned with the homomorphism of fundamental groups induced by inclusions": " Lemma 55.1. If A is a retract of X, then the homomorphism...
  17. Math Amateur

    Algebraic Topology - Fundamental Group and the Homomorphism induced by h

    On page 333 in Section 52: The Fundamental Group (Topology by Munkres) Munkres writes: (see attachement giving Munkres pages 333-334) "Suppose that h: X \rightarrow Y is a continuous map that carries the point x_0 of X to the point y_0 of Y. We denote this fact by writing: h: ( X...
  18. P

    Proving a Set in the Order Topology is Closed

    Proving a Set is Closed (Topology) Homework Statement Let Y be an ordered set in the order topology with f,g:X\rightarrow Y continuous. Show that the set A = \{x:f(x)\leq g(x)\} is closed in X. Homework Equations The Attempt at a Solution I cannot for the life of me figure...
  19. K

    Topology of real number

    consider the set P={1/n:n is counting number}, my classmate said that P is equal to (0,1] but actually i don't agree with him since (0,1] contains irrational numbers. is he correct? also, is it possible for a set not to contain both interior and boundary points?
  20. I

    Is the electron a photon with toroidal topology? - what is that?

    "Is the electron a photon with toroidal topology?" - what is that? Hello, there s a paper from 1996 http://members.chello.nl/~n.benschop/electron.pdf I have no knowledge to understand the paper, but I am very interested in how two photons can produce an electron. I would like to try to read...
  21. T

    Programs Taking Topology vs. another major for an applied math student

    Hello, I'm an undergraduate who's going to be a senior this coming fall. I'm currently triple majoring in Mathematics/Engineering Physics/Biological Engineering. I'm also looking to enter graduate school in applied mathematics. My schedule for this last year all fits together quite well, except...
  22. S

    Topology contents to be studied for higher Physics

    I have Munkres' book on Topology. For higher Physics (beyond standard model, string theory, etc.) I know we need to have an understanding of differential geometry, etc. that assume knowledge in topology. My question is how much should I study from Munkres' book? I know that it is useful to...
  23. W

    Topology question concerning global continuity of the canonical map.

    Homework Statement If the set \Z of integers is equipped with the relative topology inherited from ℝ, and κ:\Z→\Z_n (where κ is a canonical map and \Z_n is the residue class modulo n) what topology/topologies on \Z_n will render κ globally continuous? Homework Equations The Attempt...
  24. Karlx

    A good book for an introduction to Algebraic Topology

    Hi everybody. Next year I will start an undergraduate course on algebraic topology. Which book would you suggest as a good introduction to this matter ? My first options are the following: 1.- "A First Course in Algebraic Topology" by Czes Kosniowski 2.- "Algebraic Topology: An...
  25. A

    [Topology] Find the open sets in the subspace topology

    Homework Statement Suppose that (X,\tau) is the co-finite topological space on X. I : Suppose A is a finite subset of X, show that (A,\tau) is discrete topological space on A. II : Suppose A is an infinite subset of X, show that (A,\tau) inherits co-finite topology from (X,\tau). The...
  26. G

    Cofinite topology vs. Product Topology

    Homework Statement Let X be an infinite set with the cofinite topology. Show that the product topology on XxX (X cross X) is strictly finer than the cofinite topology on XxX. Homework Equations None The Attempt at a Solution So we know that a set U in X is open if X-U is finite...
  27. A

    What is general topology good for?

    I know that my question is not very clear, so I'll try my best to clarify it. Firstly, by general topology I mean point-set topology, because that's the only form of topology that I've encountered so far. In point-set topology, they teach us a lot of new definitions like open sets (that are...
  28. M

    Geometry - Topology; What is the difference?

    Geometry - Topology; "What is the difference?" It is certainly important for a good understanding of a lot of modern problems. So I think it could be important to explain clearly the difference(s) between these two notions. Can you help me?
  29. D

    Is Point-set topology worth it?

    It's an elective, I've been told that point-set topology isn't what I think it is. That is, there isn't much geometry in the introductory class and it's mostly a review of real analysis. How is the difficulty of this course? What is the typical workload? Or are these contingent upon the...
  30. Rasalhague

    Topology generated by interior operator

    Given an interior operator on the power set of a set X, i.e. a map \phi such that, for all subsets A,B of X, (IO 1)\enspace \phi X = X; (IO 2)\enspace \phi A \subseteq A; (IO 3)\enspace \phi^2A = \phi A; (IO 4)\enspace \phi(A \cap B) = \phi A \cap \phi B, I'm trying to show that the set...
  31. P

    Is this a valid argument about box topology?

    Given the following sequence in the product space R^ω, such that the coordinates of x_n are 1/n, x1 = {1, 1, 1, ...} x2 = {1/2, 1/2, 1/2, ...} x3 = {1/3, 1/3, 1/3, ...} ... the basis in the box topology can be written as ∏(-1/n, 1/n). However, as n becomes infinitely large, the basis...
  32. D

    Introduction to Topology for Analysis: Choosing the Right Textbook

    Where should I start studying topology for analysis? I'm completely new to the subject of topology, and I found there are different areas of topology, but my concern is the one that mostly maps to analysis concepts. Besides I know Munkre's Topology is the standard, but I'm not specializing in...
  33. S

    Help with Topology: Density and Customly Defined Similarity

    Homework Statement The problem is as follows: Homework Equations We are using the definition that D is dense if its closure is the whole space. Proofs using this definitions would be best as we were not taught any equivalent ones. Not sure if relevant but just in case: ~ is an...
  34. W

    Topology Help Needed: Finding Sources for Self-Taught Learners

    Hi all, From the past few days I am trying to read Kolmogorov's introductory real analysis, so far I have finished the first two chapters on set theory, metric space, but from past one week I am trying to read the third chapter on topology but this thing is going over my head, it seems so...
  35. P

    Hausdorff Space and finite complement topology

    I want to come up with examples that finite complement topology of the reals R is not Hausdorff, because by definition, for each pair x1, x2 in R, x1 and x2 have some disjoint neighborhoods. My thinking is as follows: finite complement topology of the reals R is a set that contains open sets...
  36. G

    Is it true that anything coarser than the cofinite topology is not T1 and

    ...anything finer that the cofinite topology is T1?
  37. P

    Examples of ordered topology on R x R

    I am trying to understand the difference between ordered topology and subspace topology. For one, how do I write down ordered topology of the form {1} x (1, 2] ? How do I write down a basis for {1,2} x Z_+ ?
  38. maverick280857

    Topology of Aharonov Bohm Effect - Lewis Ryder's QFT book.

    Hi, I am reading through Section 3.4 of Lewis Ryder's QFT book, where he makes the statement, This makes some sense intuitively, but can someone please explain this direct product equivalence to me as I do not have a firm background in topology (unfortunately, I need some of it for a...
  39. G

    Convergent sequences in the cofinite topology

    How can you identify the class of all sequences that converge in the cofinite topology and to what they converge to? I get the idea that any sequence that doesn't oscillate between two numbers can converge to something in the cofinite topology. Considering a constant sequence converges to the...
  40. W

    Conceptual Topology & Manifolds books

    I am looking for books that introduce the fundamentals of topology or manifolds. Not looking for proofs and rigor. Something that steps through fundamental theorems in the field, but gives conceptual explanations.
  41. C

    Applications of Topology in Physics

    Hello, I'm a physics undergrad who knows a little bit about topology (some point set, homotopy theory, and covering spaces), and I was wondering if people could describe some instances in which topology is useful for studying phenomena in physics (such as in condensed matter theory, or in...
  42. A

    Topology vs Analysis, which should be studied first?

    So I'm planning to delve into both of these subjects in some depth during the summer to prepare for undergrad analysis (using rudin) and a graduate differential topology class. My question is which one should I start out with and pay more attention to. I obviously need to study a lot of topology...
  43. M

    Sequences and convergence in the standard topology

    Hello all. I have to present a proof to our Intro to Topology class and I just wanted to make sure I did it right (before I look like a fool up there). Proposition Let c be in ℝ such that c≠0. Prove that if {an} converges to a in the standard topology, denoted by τs, then {can}...
  44. A

    Is the Proof for Cl(S ∪ T) ⊆ Cl(S) ∪ Cl(T) Correct in Topology?

    Homework Statement Cl(S \cup T)= Cl(S) \cup Cl(T)Homework Equations I'm using the fact that the closure of a set is equal to itself union its limit points.The Attempt at a Solution I am just having trouble with showing Cl(S \cup T) \subset Cl(S) \cup Cl(T). I can prove this one way, but I...
  45. J

    Are Finite Sets and the Set of All Integers in R^2 Closed?

    i have one simple question if we a consider subsets of R^2 which are: a finite set and set of all integers, then aren't a finite set and set of all integers not closed? For instance for set of all integers, it do not have any limit points. thus by definition of closed (E is closed if all...
  46. Q

    Is my understanding of open sets and bases in topology correct?

    My brain is giving me confusions. Which of these is true? 1) Given a topology T and basis B, a set U is open iff for every x in U there exists basis element B with x belonging to B, and B contained in U. 2) Given a topology T and basis B, a set U is open iff for every x in U there exists open...
  47. Fantini

    MHB Should I study metric spaces topology before general topology?

    Hello everyone. I want to study topology ahead of time (it begins next semester only) and I have two options: I could go straight for general topology (among the books I searched I found Munkres to be the one I felt most comfortable with) or go for a thorough study of metric spaces (in which...
  48. B

    Does this form a topology?

    I am told that the interval (a, ∞) where a \in (0, ∞) together the empty set and [0, ∞) form a topology on [0, ∞). But I thought in a topology that the intersection if any two sets had to also be in the topology, but the intersection of say (a, ∞) with (b, ∞) where a<b is surely (a,b) which...
  49. E

    Topology of the diffeomorphism group

    I would like to study the path components (isotopy classes) of the diffeomorphism group of some compact Riemann surface. To make sense of path connectedness, I require a notion of continuity; hence, I require a notion of an open set of diffeomorphisms. What sort of topology should I put on the...
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