A subset D of a metric space (X, d) is dense if every member of X is a limit of a sequence of elements from D.
Suppose (X,d) and (Y,ρ) are metric spaces and D is a dense subset of X.
A subset D of a metric space (X, d) is dense if every member of X...
9. Let X and Y be metric spaces, and let D be a dense subset of X. (For the definition of "dense, see Problem 4 at the end of Section 3.5.) (a) Let f : X → Y and g : X → Y be continuous functions. Suppose that f(d)gld) for all d E D. Prove that f and g are the same function.
A. Let (X, d) be a metric space so that for every E X and every r>0 the closed ball N,(z) = {ye X : d(y, z) < r} is com pact. Let be a homeomorphism. (1) Prove that f"-+m-fn。fm for all n, m E Z. (2) Let z E X and suppose that F, {fn (z) : n E 2) is a closed subset of X Prove that F is a discrete subset of X (A subset Y C...
8. [10 pts] (Carothers 7.46.) If A is a dense subset of a metric space (M, d), show that (A, d) and (M, d) have the same completion (isometrically). Hint: If M is the completion for M, then A is dense in M. Why?] Note. As in our proof of Theorem 7.18, and as Carothers does in the hint, you can take M to be a subset of M (i.e., not just isometric to one). 8. [10 pts] (Carothers 7.46.)...
2. Let (X, dx), (Y, dy) be two metric spaces, and f:X + Y a map. (a) Define what it means for the map f to be continuous at a point x E X. (b) Suppose W X is compact. Prove that then f(W) CY is compact.
(TOPOLOGY) Prove the following using the defintion: Exercise 56. Let (M, d) be a metric space and let k be a positive real number. We have shown that the function dk defined by dx(x, y) = kd(x,y) is a metric on M. Let Me denote M with metric d and let M denote M with metric dk. 1. Let f: Md+Mk be defined by f(x) = r. Show that f is continuous. 2. Let g: Mx + Md be defined...
In this problem we show that any metric space (X, d) is homeomorphic to a bounded metric space. (a) Define ρ : X X R by Show that ρ defines a metric on X. Conclude that (X,p) is a bounded metric space. (b) Show that f : (X, d) → (X, p) given by f(x) = x is a homeomorphism ism. (c) Is it true that if (X, d) is complete then (X, ρ) is complete? In this problem we...
Let X be a non-empty set. Show that the only dense subset of X with respect to the discrete metric ddise is X. The whole set of any metric spaces is always dense, so this question is really asking you to exclude all other possibilities. Show that if (X, d) is a metric space and has dense subset A + X, then (X, d) is not topologically equivalent to (X, ddisc). (Note that this is another way of showing that...
A metric space (X, d) is totally bounded if, given ε>0, there exists a finite subset = of X, called an ε-net, such that for each x∈X there exists ∈ such that d(x,) < ε. Prove that if Y is a subset of a totally bounded space X then, given ε>0, the subset Y has an ε-net and therefore Y is also totally bounded. We were unable to transcribe this imageWe were unable to transcribe this imageWe were unable to...
Let (X, d) be a discrete space and let (Y, d′) be any metric space. Prove that any function f : (X, d) → (Y, d′) is continuous. (Namely, any function from a discrete space to any metric space is continuous.)
8. A subsetD of a metric space X is dense if for all E X and all e E R+ there is an element yE D such that d(x, y) <. Show that if all Cauchy sequences (yn) from a dense set D converge in X, then X is complete.