Question

Why is $\mathcal{P}(A\cup B) \not\subset \mathcal{P}(A)\cup\mathcal{P}(B)$?

score 109 · Answer 1 · 2020-03-26 10:39:08

109

Views

Why is $\mathcal{P}(A\cup B) \not\subset \mathcal{P}(A)\cup\mathcal{P}(B)$?

Published on 26 Mar 2020 - 10:39

score 69 · Answer 2 · 2020-03-26 11:10:48

69

Views

Understanding where my naive attempt to prove Countable Choice out of Finite Choice fails

Published on 26 Mar 2020 - 11:10

score 306 · Answer 3 · 2026-03-26 02:56:03

306

Views

Why is it so difficult to prove the irrationality of the zeta function for $N$?

Published on 26 Mar 2026 - 2:56

score 20 · Answer 4 · 2020-04-04 14:54:57

20

Views

How estimate series by its own term in the Banch space?

Published on 04 Apr 2020 - 14:54

score 52 · Answer 5 · 2020-04-06 15:23:13

52

Views

What is wrong with this fake proof that any subset of a $T_1$ space is closed?

Published on 06 Apr 2020 - 15:23

score 117 · Answer 6 · 2020-04-11 22:37:05

117

Views

Prove that $\; U\setminus A = U \iff A=\emptyset\; $ where $U$ is the universe (False proof of the opposite).

Published on 11 Apr 2020 - 22:37

score 73 · Answer 7 · 2020-04-12 19:10:35

73

Views

The power of induction.

Published on 12 Apr 2020 - 19:10

score 94 · Answer 8 · 2020-04-14 12:48:48

94

Views

Likely fake proof of the irrationality of a rational multiple of pi/pi

Published on 14 Apr 2020 - 12:48

score 148 · Answer 9 · 2020-04-14 15:32:30

148

Views

Doubt in IMO 1982 problem 1

Published on 14 Apr 2020 - 15:32

score 45 · Answer 10 · 2020-04-17 01:12:54

45

Views

Find the mistake on the "proof" that $\exists x(\neg p(x)\land\neg q(x))\implies\exists x\,\neg p(x)\land\exists x\,\neg q(x)$

Published on 17 Apr 2020 - 1:12

score 184 · Answer 11 · 2020-04-18 07:04:32

184

Views

Find the mistake in the following proof by induction (exercise in AOC, Vol.1, Knuth)

Published on 18 Apr 2020 - 7:04

score 371 · Answer 12 · 2020-04-22 00:26:44

371

Views

What's wrong with this proof? if $\sum a_n$ converges and $\sum b_n$ converges absolutely, then $\sum a_nb_n$ converges

Published on 22 Apr 2020 - 0:26

score 96 · Answer 13 · 2020-04-22 05:53:48

96

Views

Showing that we can always decompose $Y = \mathbb{E}\left[Y|X\right] + \epsilon$.

Published on 22 Apr 2020 - 5:53

score 627 · Answer 14 · 2026-02-23 06:37:52

627

Views

Are two functions linearly dependent iff their Wronskian is $0$?

Published on 23 Feb 2026 - 6:37

score 53 · Answer 15 · 2020-04-23 08:12:11

53

Views

different answers for same division

Published on 23 Apr 2020 - 8:12

List Question

Why is $\mathcal{P}(A\cup B) \not\subset \mathcal{P}(A)\cup\mathcal{P}(B)$?

Understanding where my naive attempt to prove Countable Choice out of Finite Choice fails

Why is it so difficult to prove the irrationality of the zeta function for $N$?

How estimate series by its own term in the Banch space?

What is wrong with this fake proof that any subset of a $T_1$ space is closed?

Prove that $\; U\setminus A = U \iff A=\emptyset\; $ where $U$ is the universe (False proof of the opposite).

The power of induction.

Likely fake proof of the irrationality of a rational multiple of pi/pi

Doubt in IMO 1982 problem 1

Find the mistake on the "proof" that $\exists x(\neg p(x)\land\neg q(x))\implies\exists x\,\neg p(x)\land\exists x\,\neg q(x)$

Find the mistake in the following proof by induction (exercise in AOC, Vol.1, Knuth)

What's wrong with this proof? if $\sum a_n$ converges and $\sum b_n$ converges absolutely, then $\sum a_nb_n$ converges

Showing that we can always decompose $Y = \mathbb{E}\left[Y|X\right] + \epsilon$.

Are two functions linearly dependent iff their Wronskian is $0$?

different answers for same division

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