In the following exercises, consider the metric space R with the discrete metric and the subset A...
Closed sets. A subset S of a metric space M is closed, if its complement S is open. A closed ball in a metric space M, with center xo and radius r> 0, is the set of points В, (хо) %3D {x € M: d (x, хо) < r}. Problem 6.4. Prove that, for any metric space E, the entire space E is a closed set.
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...
Let (X, d) be an infinite discrete metric space. Prove that any infinite subset of X is closed and bounded but NOT compact
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....
Exercise 3. A subset A C R is said to be closed if A contains all of its limit points. A subset B CR is said to be open if its complement is a closed subset. (A) Let A CR be a closed set and let & A. Show that there is a positive 8 >0 such that A does not intersect the interval (-0,2+). (B) Let B CR be an open subset and let 3 € B. Show that...
2. Let {xn}nEN be a sequence in R converging to x 0. Show that the sequence R. Assume that x 0 and for each n є N, xn converges to 1. 3. Let A C R". Say that x E Rn is a limit point of A if every open ball around x contains a point y x such that y E A. Let K c Rn be a set such that every infinite subset of K has a limit...
4. Let Uαα∈A be a finite open cover
of a compact metric space X. For question for (a), (b)
Remark: ε is called a Lebesgue number of the cover.
(a) Show that there exists ε>0 such that for each
x∈X, the open ball B(x;ε) is contained in one of
the Uα’s.
(b) Show that if at least one of the Uα’s is a
proper subset of X, then there is a largest Lebesgue
number for the cover.
4. Let {U}aea...
The question that is being asked is Question 3 that has a red
rectangle around it.
The subsection on Question 7 is just for the Hint to part d of
Question 3.
Question 3. Lul (X', d) be a metric space. A subsct ACX is said to be Gy if there exista a collection of open U u ch that A- , , Similarly, a subact BCis said to be F if there exista collection of closed sets {F}x=1 such...
Exercise 5 (based on Tao). Let (X,d) be an arbitrary metric space. Prove the following statements (1) If a sequence is convergent in X, all its subsequences are converging to the same limit as the original sequence. (2) If a subsequence of a Cauchy sequence is convergent, then the whole sequence is convergent to the same limit as the subsequence. (3) Suppose that (X,d) is complete and Y S X is closed in (X,d). Then the space (Y,dlyxy) is complete....
Using only the definition of compact sets in a metric space, give examples of: (a) A nonempty bounded set in (R", dp), for n > 2 and 1 < pく00, which is not compact. (b) A bounded subset Y of R such that (Y, dy) contains nonempty closed and bounded subsets which are not compact (here dy is the metric inherited from the usual metric in R)
Using only the definition of compact sets in a metric space, give examples...