Question

Gap in Proof About Subsequence Converging to $\lim \sup a_n$

score 225 · Answer 1 · 2026-03-26 02:54:40

225

Views

Gap in Proof About Subsequence Converging to $\lim \sup a_n$

Published on 26 Mar 2026 - 2:54

score 77 · Answer 2 · 2026-04-09 00:54:26

77

Views

Is $\mathbb{Z} \times \mathbb{R} \subseteq \mathbb{R} \times \mathbb{Z}$ true?

Published on 09 Apr 2026 - 0:54

score 1.9k · Answer 3 · 2026-04-02 02:03:07

1.9k

Views

Right inverse implies at least a solution to AX=b and left inverse implies at most a solution to AX=b

Published on 02 Apr 2026 - 2:03

score 707 · Answer 4 · 2026-03-27 07:20:03

707

Views

Hartshorne II Prop. 6.8 (last step).

Published on 27 Mar 2026 - 7:20

score 117 · Answer 5 · 2026-03-25 18:46:32

117

Views

How to prove that it is a Cauchy sequence?

Published on 25 Mar 2026 - 18:46

score 60 · Answer 6 · 2026-03-27 22:53:10

60

Views

Asymptotics of $\sum _{n \leq x}\sigma_{-2}(n)$

Published on 27 Mar 2026 - 22:53

score 1.1k · Answer 7 · 2026-04-06 23:28:58

1.1k

Views

Prob. 8, Sec. 26, in Munkres' TOPOLOGY, 2nd ed: A map into a compact Hausdorff space is continuous iff its graph is closed

Published on 06 Apr 2026 - 23:28

score 54 · Answer 8 · 2026-04-09 07:01:53

54

Views

Understanding a proof about regular cardinals from "Set Theory for the Working Mathematician"

Published on 09 Apr 2026 - 7:01

score 26 · Answer 9 · 2018-09-26 17:13:24

If $f(x)$ is derivable over $(a,b)$, then there exsits no discontinuity point of the first kind for $f'(x)$ over $(a,b)$.

score 63 · Answer 10 · 2026-03-27 00:05:51

63

Views

If 3 is not a divisor of the order of a group, then $\forall g \in G$ $\exists h \in G$ s.t $g=h^3$

Published on 27 Mar 2026 - 0:05

score 33 · Answer 11 · 2026-04-09 14:45:52

33

Views

Verifying a fact about Connectedness

Published on 09 Apr 2026 - 14:45

score 449 · Answer 12 · 2018-09-26 21:03:29

449

Views

If $L$ is a lower bound of $S$, then $L=\inf(S)$ iff $\exists$ a sequence $\{S_n\}$ of elements of $S$ that converges to $L$

Published on 26 Sep 2018 - 21:03

score 166 · Answer 13 · 2026-04-01 18:51:12

166

Views

let $L:V \to U,$ and $M:U \to W$ be linear mappings if $M\circ L$ is one-to-one then $L$ is one-to-one

Published on 01 Apr 2026 - 18:51

score 699 · Answer 14 · 2026-03-27 02:37:38

699

Views

Solving $\int_{\Gamma}\frac{\cos(z)}{z^2(z^2+1)} \ dz$ by the Residue Theorem

Published on 27 Mar 2026 - 2:37

score 130 · Answer 15 · 2018-09-27 01:35:34

130

Views

Showing that the $\alpha$-branch of the complex square root is discontinuous at every $z \in L_\alpha$.

Published on 27 Sep 2018 - 1:35

List Question

Gap in Proof About Subsequence Converging to $\lim \sup a_n$

Is $\mathbb{Z} \times \mathbb{R} \subseteq \mathbb{R} \times \mathbb{Z}$ true?

Right inverse implies at least a solution to AX=b and left inverse implies at most a solution to AX=b

Hartshorne II Prop. 6.8 (last step).

How to prove that it is a Cauchy sequence?

Asymptotics of $\sum _{n \leq x}\sigma_{-2}(n)$

Prob. 8, Sec. 26, in Munkres' TOPOLOGY, 2nd ed: A map into a compact Hausdorff space is continuous iff its graph is closed

Understanding a proof about regular cardinals from "Set Theory for the Working Mathematician"

If $f(x)$ is derivable over $(a,b)$, then there exsits no discontinuity point of the first kind for $f'(x)$ over $(a,b)$.

If 3 is not a divisor of the order of a group, then $\forall g \in G$ $\exists h \in G$ s.t $g=h^3$

Verifying a fact about Connectedness

If $L$ is a lower bound of $S$, then $L=\inf(S)$ iff $\exists$ a sequence $\{S_n\}$ of elements of $S$ that converges to $L$

let $L:V \to U,$ and $M:U \to W$ be linear mappings if $M\circ L$ is one-to-one then $L$ is one-to-one

Solving $\int_{\Gamma}\frac{\cos(z)}{z^2(z^2+1)} \ dz$ by the Residue Theorem

Showing that the $\alpha$-branch of the complex square root is discontinuous at every $z \in L_\alpha$.

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