Topology Definition and 816 Threads

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. benorin

    Constructive Proofs Munkre's Topology Ch 1 sec. 2, ex. #1:

    Summary:: Subset of Codomain is Superset of Image of Preimage, and similar proof for subset of domain I was having a hard time doing the intro chapter's exercises in Munkres' Topology text when last I worked on it, and I just wanted to make sure that there's nothing betwixt analysis and...
  2. S

    B Topology on flat space when a manifold is locally homeomorphic to it

    [I urge the viewer to read the full post before trying to reply] I'm watching Schuller's lectures on gravitation on youtube. It's mentioned that spacetime is modeled as a topological manifold (with a bunch of additional structure that's not relevant to this question). A topological manifold is...
  3. benorin

    Munkres Topology Ch. 1 section 2 Ex #1

    Mostly I need to clear up a few basic things about functions and their inverses, the problem seems easy enough. Ok, so for (a) I have $$f^{-1}(f(A_0))= \left\{ f^{-1}(f(a)) | a\in A_0\right\}$$ but here I’m not certain if ##f^{-1}## is allowed to be multi-valued or not, the text says that if...
  4. benorin

    Munkres Topology ch1 ex #9 - Generalized DeMorgan's Laws

    So formulating them was easy, just set ##C:=D\cup E## in (1) and set ##C:=D\cap E## in (2) to see the pattern, if ##\mathfrak{B}## is a non-empty collection of sets, the generalized laws are $$A-\bigcup_{B\in\mathfrak{B}} B = \bigcap_{B\in\mathfrak{B}}(A-B)\quad (3)$$...
  5. benorin

    Munkres Topology Ch 1 ex#7) part (c) — basic set theory Q

    Obviously the parenthetical part of the definition of ##F## means ##B\subset C## but we are not allowed to use ##\subset##. I do not know how to express implication with only union, intersection, and set minus without the side relation ##B\cap C = B\Leftrightarrow B\subset C##. This is using the...
  6. diegzumillo

    I Self teaching analysis and topology

    Hi, I am a physicist interested in going through a basic analysis course. The real line, open sets, that whole thing. On my own, so I need a good selection of bibliography, ranging from those that are good references but too dense to actually read to those that are very pedagogical but tend to...
  7. Math Amateur

    I The Indiscrete Topology is Pseudometrizable ... Willard, Example 3.2(d)

    I am reading Stephen Willard: General Topology ... ... and am currently focused on Chapter 1: Set Theory and Metric Spaces and am currently focused on Section 2: Metric Spaces ... ... I need help in order to fully understand Example 3.2(d) ... .. Example 3.2(d) reads as follows: and...
  8. Math Amateur

    I Local Basis in Topology .... Definitions by Croom and Singh .... ....

    Fred H. Croom (Principles of Topology) and Tej Bahadur Singh (Elements of Topology) define local basis (apparently) slightly differently ... Croom's definition reads as follows:... and Singh's definition reads as follows: The two definitions appear different ... ... Croom requires that each...
  9. trurle

    AC-DC Power Supply Modules: Non-Isolated Topology

    In AC-DC power supply modules, having non-isolated power converter topology may result in input "Line" (hot wire) been assigned to "Vss" (lower voltage rail) at output of power supply module, and N (neutral) assigned to Vdd (upper power rail). Inside single system, this usually does not results...
  10. Math Amateur

    I The Order Topology .... .... Singh, Example 1.4.4 .... ....

    I am reading Tej Bahadur Singh: Elements of Topology, CRC Press, 2013 ... ... and am currently focused on Chapter 1, Section 1.4: Basis ... ... I need help in order to fully understand the order topology ... and specifically Example 1.4.4 ... ...Example 1.4.4 reads as follows: In order to...
  11. Math Amateur

    I Subbasis for a Topology .... Singh, Section 1.4 ....

    I am reading Tej Bahadur Singh: Elements of Topology, CRC Press, 2013 ... ... and am currently focused on Chapter 1, Section 1.4: Basis ... ... I need help in order to fully understand some remarks by Singh just before he defines a sub-basis ... .. The relevant text reads as follows: To try...
  12. V

    A Closure of constant function 1 on the complex set

    I'm watching this video to which discusses how to find the domain of the self-adjoint operator for momentum on a closed interval. At moment 46:46 minutes above we consider the constant function 1 $$f:[0,2\pi] \to \mathbb{C}$$ $$f(x)=1$$ The question is that: How can we show that the...
  13. Eclair_de_XII

    B Quick question from someone who has never taken topology

    I only took an introductory real analysis course, and that was during the spring of last year. I apologize for the unnecessary and possibly stupid question, in any case.
  14. J

    I Discrete Topology and Closed Sets

    I am trying to learn some topology and was looking at a problem in the back of the book asking to show that a topological space with the property that all set are closed is a discrete space which, as understand it, means that all possible subsets are in the topology and since all subsets are...
  15. C

    MHB Topology Munkres Chapter 1 exercise 2 e- Set theory

    Dear Everyone I am having some difficulties on exercise 2e from Topology 2nd ed by J. Munkres . Here are the directions: determine which of the following states are true for all sets A, B, C, and D. If a double implication fails, determine whether one or the other one of the possible...
  16. C

    MHB Topology Munkres Chapter 1 exercise 2 b and c- Set theory equivalent statements

    Dear Every one, I am having some difficulties on exercise 2b and 2c from Topology 2nd ed by J. Munkres . Here are the directions: determine which of the following states are true for all sets $A$, $B$, $C$, and $D$. If a double implication fails, determine whether one or the other one of the...
  17. D

    I How Does Vector Subtraction Relate to Topology?

    I learned in a vector calculus class that the operation of vectors is not defined. The professor mentioned it had to do with topology. How does the operation of vector subtraction relate to topology and how does topological properties prevent vector subtraction from being defined?
  18. Math Amateur

    MHB Understand Example 3.10 (b) Karl R. Stromberg, Chapter 3: Limits & Continuity

    I am reading Karl R. Stromberg's book: "An Introduction to Classical Real Analysis". ... ... I am focused on Chapter 3: Limits and Continuity ... ... I need help in order to fully understand Example 3.10 (b) on page 95 ... ... Example 3.10 (b) reads as follows: My question is as...
  19. Math Amateur

    MHB Understanding Topology: Closure, Boundary & Open/Closed Sets

    I am reading Andrew Browder's book: "Mathematical Analysis: An Introduction" ... ... I am reading Chapter 6: Topology ... ... and am currently focused on Section 6.1 Topological Spaces ... I need some help in order to fully understand a statement by Browder in Section 6.1 ... ... The...
  20. M

    A Vector space (no topology) basis

    The standard definition of the basis for a vector space is that all the vectors can be defined as finite linear combinations of basis elements. Consider the vector space consisting of all sequences of field elements. Basis vectors could be defined as vectors which are zero except for one term in...
  21. J

    A Topology in Physics: Exploring Uses in Physics

    How are topological spaces used in physics?
  22. cianfa72

    I Product Space vs Fiber Bundle: Understanding the Difference

    Hi, I'm not a really mathematician...I've a doubt about the difference between a trivial example of fiber bundle and the cartesian product space. Consider the product space ## B \times F ## : from sources I read it is an example of trivial fiber bundle with ##B## as base space and ##F## the...
  23. AryaKimiaghalam

    Courses Taking an introductory topology course for physics

    Hello,I'm a freshman undergraduate physics student. I'm mainly considering theoretical physics for graduate school (condensed matter and AMO physics). There is an introductory topology course at my university which is offered by the math department. Will taking topology be useful for any...
  24. R

    Continuity of a function under Euclidean topology

    Homework Statement Let ##f:X\rightarrow Y## with X = Y = ##\mathbb{R}^2## an euclidean topology. ## f(x_1,x_2) =( x^2_1+x_2*sin(x_1),x^3_2-sin(e^{x_1+x_2} ) )## Is f continuous? Homework Equations f is continuous if for every open set U in Y, its pre-image ##f^{-1}(U)## is open in X. or if...
  25. T

    B Algebraic Topology in the tv show The Big Bang Theory

    in the tv show "The Big Bang Theory", Sheldon wrote a book called "A proof the algebraic topology can never have a non self-contradictory set of abelian groups". Is this just a random set of words that is meant to sound smart but in reality means nothing or is it accurate? If it is, what does it...
  26. L

    A Structure preserved by strong equivalence of metrics?

    Let ##d_1## and ##d_2## be two metrics on the same set ##X##. We say that ##d_1## and ##d_2## are equivalent if the identity map from ##(X,d_1)## to ##(X,d_2)## and its inverse are continuous. We say that they’re uniformly equivalent if the identity map and its inverse are uniformly...
  27. L

    A Same open sets + same bounded sets => same Cauchy sequences?

    Let ##d_1## and ##d_2## be two metrics on the same set ##X##. Suppose that a set is open with respect to ##d_1## if and only if it is open with respect to ##d_2##, and a set is bounded with respect to ##d_1## it and only if it is bounded with respect to ##d_2##. (In technical language, ##d_1##...
  28. M

    I Why can't I reach every cell in a 3x3 square?

    Hi, I was playing this game in which you start from any cells of a 3x3 or 5x5 square and draw a line that loops through every cell in the box. The line can go only through a vertical or horizontal side (not diagonally). When you start from certain cells (problem cells), you can't reach at...
  29. Cantor080

    I Topology Words: Reasons for the particular names

    From Munkres, Topology: "A topology on a set X is a collection T of subsets of X having the following properties: (1) ∅ and X are in T . (2) The union of the elements of any subcollection of T is in T . (3) The intersection of the elements of any finite subcollection of T is in T . A set X for...
  30. CaptainAmerica17

    B Spivak's Calculus as a Prerequisite for General Topology

    High school student here... Recently, I've found an interest in topology and am trying to figure out the correct path for self-studying. I am familiar with set theory and some concepts of abstract algebra but have not really studied any form of analysis, which from what I've read is a...
  31. Mr Davis 97

    I Metric Spaces and Topology in Analysis

    I'm beginning to study analysis beyond real numbers, but I am a but confused. What is the relation between topology, metric spaces, and analysis? From what it seems, it's that metric space theory forms a subset of topology, and that analysis uses the metric space notion of distance to describe...
  32. Gene Naden

    I How to prove that compact regions in surfaces are closed?

    This is problem 4.7.11 of O'Neill's *Elementary Differential Geometry*, second edition. The hint says to use the Hausdorff axiom ("Distinct points have distinct neighborhoods") and the results of fact that a finite intersection of neighborhoods of p is again a neighborhood of p. Here is my...
  33. YoungPhysicist

    Which function drawer is this one?

    Have anybody seen a 3D function drawer like this one?(4:12) Since I don’t know what these 3D drawers are really called,I can’t find any.
  34. ubergewehr273

    Question about a function of sets

    Let a function ##f:X \to X## be defined. Let A and B be sets such that ##A \subseteq X## and ##B \subseteq X##. Then which of the following are correct ? a) ##f(A \cup B) = f(A) \cup f(B)## b) ##f(A \cap B) = f(A) \cap f(B)## c) ##f^{-1}(A \cup B) = f^{-1}(A) \cup f^{-1}(B)## d) ##f^{-1}(A \cap...
  35. diegzumillo

    A Graph or lattice topology discretization

    Mathematicians, I summon thee to help me identify which field deals with this stuff. I come here not as a physicist but as a sunday programmer trying to solve some numerical problems. I set out to model a lattice version of a smooth space. A discretization procedure not uncommon in physics, but...
  36. C

    A Physics of Topological Insulators and Superconductors

    Hello there! Topological insulators and supercontuctors nowadays are very active field in physics research. I am looking for a Phd in theoretical matter physics, and these arguments could interest me. But I have a question: phisicists that study topological superconductors, insulators and...
  37. N

    A Topology of Black Holes: Decomposing the Manifold and the Role of Knots

    Can a black hole be presented as a Heegaard decomposition or as the complement of a knot? I'll try and elaborate: If I understand correctly, the cross section of spacetime near a black hole can be thought of topologically as a manifold. What manifold is it? Can the manifold be decomposed?
  38. Bill2500

    I Topology vs Differential Geometry

    Hello. I am studying Analysis on Manifolds by Munkres. My aim is to be able to study by myself Spivak's Differential Geometry books. The problems is that the proof in Analysis on Manifolds seem many times difficult to understand and I am having SERIOUS trouble picturing myself coming up with...
  39. K

    I Topology Usefulness: Exploring an Example

    I was asking to myself what is the usefulness of a topology. I'd thought this question before and couldn't find results on the literature, perhaps I was not searching with the right terms. So I started thinking that maybe a topology is a way of defining the domain, codomain and image of a...
  40. mr.tea

    I Baire Category Theorem: Question About Countable Dense Open Sets

    Hi, I have a (probably stupid) question about the Baire Category Theorem. I am looking at the statement that says that in a complete metric space, the intersection of countable many dense open sets is dense in the metric space. Assume that we have the countable collection of dense open sets ##...
  41. mr.tea

    Topology What is a Good Supplementary Book for Topology Beyond Theorem, Proof?

    I am taking a course in topology with Gamelin and Greene, Introduction to topology. I would like to have some supplement to extend and give more motivation and explanation. I am quite tired of the "theorem, proof, theorem, proof" pattern. Thank you!
  42. facenian

    Is Every Connected Metric Space Compact?

    Homework Statement This is a problem from Munkres(Topology): Show that a connected metric space ##M## having having more than one point is uncountable. Homework Equations A theorem of that section of the book states: Let ##X## be a nonempty compact Hausdorff space. If no singleton in ##X## is...
  43. mr.tea

    I Defining Neighborhoods in Topology: Inclusion vs. Containment

    Hi,t I am studying topology at the moment. I have seen that some authors define the neighborhood of a point using inclusion of an open set, while others define the term as open set that contains the point. In most of the theory I have seen so far, the latter is more convenient to use. Why is...
  44. Another

    I What are the essential foundations for studying topology?

    To start studying topology, what basic knowledge should I have?
  45. A

    I Proving that an action is transitive in the orbits

    <Moderator's note: Moved from General Math to Differential Geometry.> Let p:E→ B be a covering space with a group of Deck transformations Δ(p). Let b2 ∈ B be a basic point. Suppose that the action of Δ(p) on p-1(b0) is transitive. Show that for all b ∈ B the action of Δ(p)on p-1(b) is also...
  46. K

    I R is disconnected with the subspace topology

    I want to show that ##\mathbb{R}## is disconnected with the subspace topology. For this I considered that ##\mathbb{R} = \lim_{\delta n \longrightarrow 0 } (-\infty, n] \cup [n+\delta n, \infty)## and of course the intersection of these two open sets is empty. What I'm not sure is about the...
  47. K

    I Topology: Can We Use Same Function for 2 Open Sets?

    In reading out about topological spaces and topologies I noticed that they do not give much specific examples, so I have not found an answer to the following simple question: Can we use the same function for mapping into two different open sets of a given topology? Or, perhaps equivalently, can...
  48. K

    I Exploring the Origins of Topology Axioms

    Is there a way we can see why the axioms defining a topology/ topological space are the way they are?
  49. M

    Geometry Textbook recommendations on geometry & topology

    Hello fellows My background is architecture (bachelor in2016) but for unknown reasons I’ve been fascinated by geometry since last year. it was roughly at the stage where I was trying to grasp ‘the truth ‘ of architecture and somehow got into geometry... happy coincidence. Since I hadn’t...
  50. Observeraren

    I Turning the square into a circle

    Hello Forum, Does topology reckon the art of turning a square into a circle? I am quite new to topology and maths in general, I have only dabbled and eyed on my collection of mathbooks. I have come to a conclusion of how to turn the Square into A Circle without cutting. I wonder if I am...
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