4. Let A, B CR be non-empty open sets. Prove that AU B is an open...
Prove: Let A be a dense subset of (X, T), and let B be a non-empty open subset of X. Then An B Prove: Let A be a dense subset of (X, T), and let B be a non-empty open subset of X. Then An B
Let A and B be two non-empty bounded sets, and A and B are disjoint. Is sup(A U B) = sup(A) + sup(B)? Prove if true, and give a counter example if not.
4. Let A, B, and C be sets. Prove that AU(BNC) = (AUB) n (AUC).
4. Let A be a non-empty set and f: A- A be a function. (a) Prove that f has a left inverse in FA if and only if f is injective (one-to-one) (b) Prove that, if f is injective but not surjective (which means that the set A is infinite), then f has at least two different left inverses.
4·Let A and B be non-empty subsets of a space X. Prove that A U B is disconnected if A n B)U(A nB) 0. Prove that X is connected if and only if for every pair of non-empty subsets A and B of X such that X A U B we have (A B)U (An B)O.
1. Let A, B be two non-empty sets and f: A + B a function. We say that f satisfies the o-property if VC+0.Vg, h: C + A, fog=foh=g=h. Prove that f is injective if and only if f satisfies the o-property.
Looking for full solutions of question (a)(b)and(c) Problem 4. Let A CR. Given any a, b € R, with a <b, define (a,b) A = {2 € A:a < x <b}. We call (a, b) A an open interval in A (or an open interval relative to A). a) Show that (a, b) A = (a,b) n A. b) Prove that a set V C A is relatively open in A if and only if for every 3 EV, there...
1. (a) Let d be a metric on a non-empty set X. Prove that each of the following are metrics on X: a a + i. d(1)(, y) = kd(x, y), where k >0; [3] ii. dr,y) d(2) (1, y) = [10] 1+ d(,y) The proof of the triangle inequality for d(2) boils down to showing b + > 1fc 1+a 1+b 1+c for all a, b, c > 0 with a +b > c. Proceed as follows to prove...
hal 5. Let CR denote the r Prove curve 1«R for some R21 au alying on Ce. hal 5. Let CR denote the r Prove curve 1«R for some R21 au alying on Ce.
Let A, B be non-empty, bounded subsets of R. a) If the statement is true, prove it. If the statement is false, give a counterexample: sup(AUB) = max(sup(A), sup(B)}. b) If the statement is true, prove it. If the statement is false, give a counterexample: If An B + Ø, then sup(A n B) = min{sup(A), sup(B)}. E 选择文件