Problem 1. Let (X, d) be a metric space and t the metric topology on X. (a) Fix a E X. Prove that the map f :(X, T) + R defined by f(x) = d(a, x) is continuous. (b) If {x'n} and {yn} are Cauchy sequences, prove that {d(In, Yn)} is a Cauchy sequence in R.
#9. all one problem.
then e is 0U tric space. Show that there is an isometric imbedding h of X 、D), as follows: Let X denote the set of all space () into a complete metric Cauchy sequences of points of X. Define x~ y if Let [x] denote the equivalence class of x; and let Y denote the set of these eq x (xi, x2, ...) uiv alence classes. Define a metric D on Y by the equation linnod(xn,...
5. Let X be a metric space. (a) Let x E X be an isolated point. Prove that the only sequences in X that converge to a are the sequences that are eventually constant (b) Prove that the only convergent sequences in a discrete metric space (See Problem 8 on page 79 for the definitions of "isolated" and "discrete.") with tail a,z,x.... are the eventually constant sequences.
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.
1. Prove that if f : D -» Y is uniformly continuous then there exists an extension15 of f to a if dn (E D) e X define 7(x) lim f(d,) uniformly continuous function f:X * Y. Hint: 2....
Question 1. Give an example of a complete metric space (X, d) and a function f :X + X such that d(f(x), f(y)) < d(x, y) for all x, y E X with x + y and yet f does not have a fixed point. a map f:X + X has a fixed point if there is an element a E X such that f(a) = a.
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...
Problem 2: For any x, y e R let d(x,y):-arctan(y) - arctan(x). Do the following: (1) Prove that d is a metric on R. (2) Letting xnn, prove that {xnJnE is a Cauchy sequence with no limit in R (Note that {xn)nen is NOT Cauchy under the Euclidean metric and that all Cauchy sequences in the Euclidean metric have a limit in R.)
Problem 2: For any x, y e R let d(x,y):-arctan(y) - arctan(x). Do the following: (1) Prove...
In the following, (X,d) is an arbitrary metric space and (X,d,μ)
is an arbitrary metric measure space.
(6) Recall the definition of bounded set: The set A C (X, d) is bounded if δ(A) < 00 where 6(A)p d(a,a). (X,d) with ACBand B is bounded then A is bounded (a) Show that if A, B (b) Fix a set A. I B - (r), a single point, show that D(A, B)-0 if and only f (c) Prove that the function...
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.)...
Q3 * You are given two subsets A, B C M of a metric space M. Define p by p=inf{d(x, y)| 2 € A, Y E B}. Prove that, if p > 0 then A and B are separated. Give an example where p=0, but A and B are not separated. Q4 Show that Q as a subset of R is disconnected. Likewise show R Q is disconnected.