Question

Prove for each of the following:

a. Exercise A union of finitely many or countably many countable sets is countable. (Hint: Similar)

b. Theorem: (Cantor 1874, 1891) R is uncountable.

c. Theorem: We write |R| = c the “continuum”. Then c = |P(N)| = 2א0

d. Prove the set I of irrational number is uncountable. (Hint: Contradiction.)

Answer #1

a) Prove that the union between two countably infinite sets is a
countably infinite set.
b) Would the statement above hold if we instead started with an
infinite amount of countably infinite sets?
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Thank you in advance!

Prove that a countable union of countable sets countable; i.e.,
if {Ai}i∈I is a collection of sets, indexed by I ⊂ N, with each Ai
countable, then union i∈I Ai is countable. Hints: (i) Show that it
suffices to prove this for the case in which I = N and, for every i
∈ N, the set Ai is nonempty. (ii) In the case above, a result
proven in class shows that for each i ∈ N there is a...

Which of the following sets are finite? countably infinite?
uncountable? Give reasons for your answers for each of the
following:
(a) {1\n :n ∈ Z\{0}};
(b)R\N;
(c){x ∈ N:|x−7|>|x|};
(d)2Z×3Z
Please answer questions in clear hand-writing and show me the
full process, thank you (Sometimes I get the answer which was
difficult to read).

For each of the following sets, determine whether they are
countable or uncountable (explain your reasoning). For countable
sets, provide some explicit counting scheme and list the first 20
elements according to your scheme. (a) The set [0, 1]R ×
[0, 1]R = {(x, y) | x, y ∈ R, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1}.
(b) The set [0, 1]Q × [0, 1]Q = {(x, y) |
x, y ∈ Q, 0 ≤ x ≤...

Using field axioms and order axioms prove the following
theorems
(i) The sets R (real numbers), P (positive numbers) and [1,
infinity) are all inductive
(ii) N (set of natural numbers) is inductive. In particular, 1
is a natural number
(iii) If n is a natural number, then n >= 1
(iv) (The induction principle). If M is a subset of N (set of
natural numbers) then M = N
The following definitions are given:
A subset S of R...

Using field and order axioms prove the following theorems:
(i) Let x, y, and z be elements of R, the
a. If 0 < x, and y < z, then xy < xz
b. If x < 0 and y < z, then xz < xy
(ii) If x, y are elements of R and 0 < x < y, then 0 <
y ^ -1 < x ^ -1
(iii) If x,y are elements of R and x <...

You’re the grader. To each “Proof”, assign one of the following
grades:
• A (correct), if the claim and proof are correct, even if the
proof is not the simplest, or the proof you would have given.
• C (partially correct), if the claim is correct and the proof
is largely a correct claim, but contains one or two incorrect
statements or justications.
• F (failure), if the claim is incorrect, the main idea of the
proof is incorrect, or...

1. Write the following sets in list form. (For example, {x | x
∈N,1 ≤ x < 6} would be {1,2,3,4,5}.) (a) {a | a ∈Z,a2 ≤ 1}. (b)
{b2 | b ∈Z,−2 ≤ b ≤ 2} (c) {c | c2 −4c−5 = 0}. (d) {d | d ∈R,d2
< 0}.
2. Let S be the set {1,2,{1,3},{2}}. Answer true or false: (a) 1
∈ S. (b) {2}⊆ S. (c) 3 ∈ S. (d) {1,3}∈ S. (e) {1,2}∈ S (f)...

Write a program of wordSearch puzzle that use
the following text file as an input. The output should be like
this: PIXEL found (left) at (0,9). ( Use
JAVA Array ) .Please do not use
arrylist and the likes!
Hints
• The puzzle can be represented as a right-sized two-dimensional
array of characters (char).
• A String can be converted into a right-sized array of characters
via the String method toCharArray.
. A word can occur in any of 8...

2. Which of the following is a negation for ¡°All dogs are
loyal¡±? More than one answer may be correct.
a. All dogs are disloyal. b. No dogs are loyal.
c. Some dogs are disloyal. d. Some dogs are loyal.
e. There is a disloyal animal that is not a dog.
f. There is a dog that is disloyal.
g. No animals that are not dogs are loyal.
h. Some animals that are not dogs are loyal.
3. Write a...

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