What is Topology: Definition and 808 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. D

    Prove the function is continuous (topology)

    Homework Statement Let X be the set of continuous functions ## f:\left [ a,b \right ] \rightarrow \mathbb{R} ##. Let d*(f,g) = ## \int_{a}^{b}\left | f(t) - g(t) \right | dt ## for f,g in X. For each f in X set, ## I(f) = \int_{a}^{b}f(t)dt ## Prove that the function ## I ##...
  2. 1

    Proof of convergence (intro topology)

    Homework Statement Show that if x = (x1, x2,...) and y = (y1, y2,...) are members of l^2, then \sum^{\infty}_{i=1} |x_{i}y_{i}| Converges Homework Equations My book defines l^2 to be: { x=(x_{1}, x_{2}, ... ) \in ℝ^{\omega} : \sum^{\infty}_{i=1} (x_{i})^{2} converges }...
  3. 1

    Some introductory Topology questions

    Hi all, My Topology textbook arrived in the mail today, so I started reading it. It begins with an introduction to an object called metric spaces. It says A metric on a set X is a function d: X x X -> R that satisfies the following conditions: -some conditions-- I am not...
  4. J

    Topology problem about Hausdorff space and compactness

    Would anyone have ideas on how to solve the following problem? Let (X, τ) be a Hausdorff space and τ0 = {X\K: so that K is compact in (X, τ)} Show that: 1) τ0 is a topology of X. 2) τ0 is rougher than τ (i.e. τ0 is a genuine subset of τ). 3) (X, τ0) is compact. This was a...
  5. H

    Proving Proposition: Quotient Space Rn/F is First Countable

    Hi, I am trying to prove the following proposition: Let F be a closed subset of the Euclidean space Rn.Then the quotient space Rn/F is first countable if and only if the boundary of F is bounded in Rn. Any ideas?
  6. N

    Topology of punctured plane vs topology of circle?

    So how does the topology of R^n minus the origin relate to that of the (n-1)-dimensional sphere? I would think the topology of the former is equivalent to that of an (n-1)-dimensional sphere with finite thickness, and open edges. But I suppose that is as close as one can get to the...
  7. T

    Show that B is not a topology on R

    Homework Statement Let B be the family of subsets of \mathbb{R} consisting of \mathbb{R} and the subsets [n,a) := {r \in \mathbb{R} : n \leq r < a} with n \in \mathbb{Z}, a \in \mathbb{R} Show that B is not a topology on \mathbb{R} Homework Equations The Attempt at a Solution If B...
  8. S

    Subspace Topology on A: Calculate T_A

    Homework Statement 1. Let A= {a,b,c}. Calculate the subspace topology on A induced by the topology T= { empty set, X,{a},{c,d},{b,c,e},{a,c,d},{a,b,c,e},{b,c,d,e},{c}, {a,c}} on X={a,b,c,d,e}.Homework Equations Given a topological space (X, T) and a subset S of X...
  9. V

    How useful is topology in physics?

    Whenever I try to understand deeper aspects of the higher maths involved in physics I keep hearing about topology related stuff. How useful is it to learn topology in order to get a deeper understanding on the maths behind physics? Also, what other maths should I look into? Functional analysis...
  10. ArcanaNoir

    Arithmetic progression topology, Z not compact

    Homework Statement The Dirichlet Prime Number Theorem indicates that if a and b are relatively prime, then the arithmetic progression A_{a,b} = \{ ...,a−2b,a−b,a,a+b,a+2b,...\} contains infinitely many prime numbers. Use this result to prove that Z in the arithmetic progression topology is not...
  11. S

    Subspace topology and Closed Sets

    Homework Statement Hi, This is my first post. I had a question regarding open/closed sets and subspace topology. Let A be a subset of a topological space X and give A the subspace topology. Prove that if a set C is closed then C= A intersect K for some closed subset K of X. Homework...
  12. B

    Topology, lemiscate not an embedded submanifold

    Homework Statement Show that the image of the curve Let β: (-π,π) → ℝ2 be given by β(t) = (sin2t, sint) is not an embedded submanifold of ℝ2Homework Equations The Attempt at a Solution So I'm not too great with the topology. I do see that β'(t) = (2cos2t, cost) ≠ 0 for all t. So β is a...
  13. B

    Graphs of Continuous Functions and the Subspace Topology

    Let U be a subset of ℝn be an open subset and let f:U→ℝk be a continuous function. the graph of f is the subset ℝn × ℝk defined by G(f) = {(x,y) in ℝn × ℝk : x in U and y=f(x)} with the subspace topology so I'm really just trying to understand that last part of this definition...
  14. G

    Discrete topology and discrete subspaces

    Homework Statement If A is a subspace of X and A has discrete topology does X have discrete topolgy?Also if X has discrete topology then does it imply that A must have discrete topology? The Attempt at a Solution My understanding of discrete topology suggests to me that if A is discrete it...
  15. F

    Non-trivial Topology: Definition & Explanation

    Hi there, I've come across the term 'non-trivial topology' or 'non-trivial surface states' when researching topological superconductors and really need a bit of help as to exactley what this means? I've tried google but no-one seems to give a definition? Many thanks for checking this out
  16. D

    Functional analysis and topology books needed

    Hi folks ... I urgently need good books about Functional analysis and Topology. These must be comprehensive and thorough, undergraduate or graduate. Please, advise and provide your experiences with such books. I accept only thick books ;) e.g Introductory Functional Analysis with...
  17. R

    Does This Sequence Converge in the 5-adic Metric?

    Metric Space and Topology HW help! Let X be a metric space and let (sn )n be a sequence whose terms are in X. We say that (sn )n converges to s \ni X if \forall \epsilon > 0 \exists N \forall n ≥ N : d(sn,s) < \epsilon For n ≥ 1, let jn = 2[(5^(n) - 5^(n-1))/4]. (Convince yourself...
  18. tsuwal

    Metric Spaces: Exercise 1.14 from Introduction to Topology (Dover)

    Homework Statement X is a metric and E is a subspace of X (E\subsetX) The boundary ∂E of a set E is defined to be the set of points adherent to both E and the complement of E, ∂E=\overline{E}\cap(\overline{X\E}) (ignore the red color, i can't get it out) Show that E is open if and only...
  19. K

    Is There an Easier Way to Prove S is Disconnected?

    Homework Statement Let S={zεℂ: |z|<1 or |z-2|<1}. show that S is not connected.Homework Equations My prof use this definition of disconnected set. Disconnected set - A set S \subseteqℂ is disconnected if S is a union of two disjoint sets A and A' s.t. there exists open sets B and B' with A...
  20. micromass

    Topology Introduction to Topology by Mendelson

    Author: Bert Mendelson Title: Introduction to Topology Amazon link: https://www.amazon.com/dp/0486663523/?tag=pfamazon01-20 Level: Undergrad
  21. B

    Topology, line with two origins

    Homework Statement Let X be the set of all points (x,y)\inℝ2 such that y=±1, and let M be the quotient of X by the equivalence relation generated by (x,-1)~(x,1) for all x≠0. Show that M is locally Euclidean and second-countable, but not Hausdorff. Homework Equations The Attempt at...
  22. micromass

    Topology Topology from the Differentiable Viewpoint by Milnor

    Author: John Milnor Title: Topology from the Differentiable Viewpoint Amazon Link: https://www.amazon.com/dp/0691048339/?tag=pfamazon01-20 Prerequisities: Level: Undergrad Table of Contents: Preface Smooth manifolds and smooth maps Tangent spaces and derivatives Regular values The...
  23. micromass

    Topology Differential Forms in Algebraic Topology by Bott and Tu

    Author: Raoul Bott, Loring Tu Title: Differential Forms in Algebraic Topology Amazon Link: https://www.amazon.com/dp/1441928154/?tag=pfamazon01-20 Prerequisities: Differential Geometry, Algebraic Topology Level: Grad Table of Contents: Introduction De Rham Theory The de Rham Complex...
  24. D

    Topology on Eculidean n-space(ℝ^n)

    Hey guys in fact here is my first time to have interaction over this forum! I've already read how one can show the topology in ℝ(real Line) which is usual called standard topology fulfill the three condition fro to be topology. however, I want to make inquiry on how can i proof whether...
  25. D

    Is the Unit Interval [0,1] Open in Its Inherited Topology from the Real Line?

    Hi all, I need help with something basic but I'm not sure how to handle it. The doubt is about how to consider the topology of the unit interval I=[0,1] inherited of the real line with its usual topology (intervals of the type (a,b)). I think that is just to pay attention to the definition...
  26. ArcanaNoir

    Hausdorff topology on five-element set that is not the discrete top.

    Homework Statement The textbook exercise asks for a Hausdorff topology on \{a,b,c,d,e\} which is not the discrete topology (the power set). It is from "Introduction to Topology, Pure and Applied", by Adams and Franzosa. Homework Equations Let X be a set. Definition of topology...
  27. L

    Basic topology proof of closed interval in R

    Let \{ [a_j, b_j]\}_{j\in J} be a set of (possibly infinitely many closed intervals in R whose intersection cannot be expressed as a disjoint union of subsets of R. Prove that \bigcup\limits_{j \in J} {\{ [{a_j},{b_j}]\} } is a closed interval in R. I don't understand how to attack this...
  28. micromass

    Topology Topology by James Munkres | Prerequisites, Level & TOC

    Author: James Munkres Title: Topology Amazon link https://www.amazon.com/dp/0131816292/?tag=pfamazon01-20 Prerequisities: Being acquainted with proofs and rigorous mathematics. An encounter with rigorous calculus or analysis is a plus. Level: Undergrad Table of Contents: Preface A Note...
  29. D

    How is a discrete topology a 0-manifold?

    I am new to manifolds and I read the fact that any discrete space is a 0 dimensional manifold. I am having a hard time understanding why and feel this is very basic. So to be a manifold, each point in the space should have a neighborhood about it that is homeomorphic to R^n. (and n will...
  30. S

    Munkres Topology - Chapter 7 - Complete Metric Spaces and Function Spaces

    Hello, I was wondering if it was possible (or advisable) to read Chapter 7 of Munkres (Complete Metric Spaces and Function Spaces) without having done Tietze Extension Theorem, the Imbeddings of Manifolds section, the entirety of Chapter 5 (Tychonoff Theorem) and the entirety of Chapter 6...
  31. K

    Recommended Set Theory Textbooks for Studying Topology and Beyond

    I'm a physics undergraduate and I'll starting learning topology from Munkres next semester. But first I want to learn set theory to feel more comfortable. Do you know any good textbook? A friend of mne from the math department said I should go with Kaplansky's "Set Theory and Metric Spaces".
  32. B

    Closure in Topology and Algebra

    In topology, when we say a set is closed, it means it contains all of its limit points In Algebra closure of S under * is defined as if a, b are in S then a*b is in S. Are these notations similar in any way?
  33. K

    The Topology of Spacetimes: Exploring the Global Structure of Curved Manifolds

    Mod note: This thread contains an off-topic discussion from the thread https://www.physicsforums.com/showthread.php?p=4216768 So a notion of distance is used... I wonder how.
  34. J

    Question concerning a topology induced by a particular metric.

    The question comes from the Munkres text, p. 133 #3. Let Xn be a metric space with metric dn, for n ε Z+. Part (a) defines a metric by the equation ρ(x,y)=max{d1(x,y),...,dn(x,y)}. Then, the problem askes to show that ρ is a metric for the product space X1 x ... x Xn. When I originally...
  35. M

    Good books in topology for beginners ?

    which books do you think are good to beginners in topology ? for someone don't know any thing in topology and little set theory ?
  36. T

    Do you prefer Topology or Algebra?

    To all who have taken an introduction course to topology and abstract algebra, which did you prefer and why? Does the preference of one course over the other reflect a certain from of intuition that we rely on for reasoning or heuristics for problem solving? For these classes, I used...
  37. M

    Criticize my proof (metric topology, Munkres)

    Homework Statement Let ##X## be a metric space with metric ##d##. Show that ##d: X \times X \mapsto \mathbb{R}## is continuous.Homework Equations The Attempt at a Solution Please try to poke holes in my proof, and if it is correct, please let me know if there's any more efficient way to do it...
  38. M

    Explanation of uniform topology theorem in Munkres

    Hi all, I'm looking for some help in understanding one of the theorems stated in section 20 of Munkres. The theorem is as follows: The uniform topology on ##\mathbb{R}^J## (where ##J## is some arbitrary index set) is finer than the product topology and coarser than the box topology; these...
  39. D

    Subspace topology of Rationals on Reals

    I am trying to visualize the subsppace topology that is generated when you take the Rationals as a subset of the Reals. So if we have ℝ with the standard topology, open sets in a subspace topology induced by Q would be the intersection of every open set O in ℝ with Q. Since each open set...
  40. J

    Is the set {a} x (a,b) open in R x R in the dictionary order topology?

    I want to say yes. I am having trouble convincing myself though. Can anyone give me a very small nudge in the right direction? Thanks!
  41. M

    Proof check: continuous functions (General topology)

    Homework Statement Let ##A \subset X##; let ##f:A \mapsto Y## be continuous; let ##Y## be Hausdorff. Show that if ##f## may be extended to a continuous function ##g: \overline{A} \mapsto Y##, then ##g## is uniquely determined by ##f##. Homework Equations The Attempt at a Solution...
  42. J

    Algebraic Topology: Connected Sum & Reference Help

    I was working on some algebraic topology matters, thinkgs like the connected sum of some surfaces is some other surface. And for this study, I was using the Munkres's famous textbook 'Topology' the algebraic topology part. My qeustions are as follows: Q1) Munkres introduces 'labelling scheme'...
  43. S

    Finding Planar Representation of Torus with n Holes

    Homework Statement Find the fundamental group of T^{n}, the torus with n holes, by finding the planar representation of T^{n}. Homework Equations I'm just having a hard time finding the planar representation of T^{n}. I can't picture it.The Attempt at a Solution I can see how the picture...
  44. S

    Quotient Topology and Adjunction Space

    Does anyone have any good reference to exercises concerning these topics? I would like to understand them better. Thank you.
  45. R

    Basic topology - Limit points and closure

    This isn't really hw, just me being confused over some examples. I have 'learned' the basic definitions of neighborhood, limit point, closed, and closure but have some trouble accepting the following examples. 1. For Q in R, Q is not closed. The set of all limit points of Q is R, so its...
  46. P

    Thoughts on Henle's Topology book?

    Hi all! I'd like to ask for some opinions on a book. I'm currently taking an undergraduate course in topology. We're using the book A Combinatorial Introduction to Topology, by Michael Henle, and so far I have mixed feelings about it, feelings that my class and professor seem to share. 1...
  47. D

    Continuous mappings in topology.

    I am trying to understand the theorem: Let f:S->T be a transformation of the space S into the space T. A necessary and sufficient condition that f be continuous is that if O is any open subset of T, then its inverse image f^{-1}(O) is open in S. First off, I don't really understand what...
  48. CJ2116

    Topology and Differential Geometry texts for General Relativity

    Hi everyone, I was wondering if I could some advice from anyone who has some experience with higher level general relativity. Any help would be greatly appreciated! Some background: I'm currently working through Robert Wald's General Relativity and am struggling a lot with the "advanced...
  49. H

    Prove every Hausdorff topology on a finite set is discret.

    Homework Statement Prove that every Hausdorff topology on a finite set is discrete. I'm trying to understand a proof of this, but it's throwing me off--here's why: Homework Equations To be Hausdorff means for any two distinct points, there exists disjoint neighborhoods for those points...
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