User Math_Images_Only

7 votes

1 answer

103 views

Finding where in Ramsey's theorem one uses the Axiom of choice

asked May 12 at 15:09

5 votes

0 answers

96 views

Examples of Substructures that "do not know they are that substructure"

soft-question set-theory model-theory

asked May 12 at 21:29

4 votes

0 answers

123 views

Proof that $G_\delta$ sets in $\mathbb{R}$ are either countable,finite, or have cardinality of the continuum.

set-theory trees descriptive-set-theory

asked Jun 20, 2021 at 16:31

4 votes

2 answers

266 views

If $\kappa=\kappa^{<\kappa}$ then there is a dense linear order of size $\kappa$ in which all ordinals $<\kappa^+$ can embed.

solution-verification set-theory cardinals

asked Aug 11, 2021 at 11:01

4 votes

2 answers

361 views

Proof that the quotient space of $\mathbb{R}^2/L$ where $L$ is a line passing through the origin is not first countable

general-topology quotient-spaces first-countable

asked Nov 4, 2019 at 15:22

4 votes

2 answers

638 views

Proof Cancellation property in lattice implies distributivity

order-theory lattice-orders

asked Feb 9, 2020 at 3:15

3 votes

1 answer

176 views

Derivative of generalized Taylor expansion of a function between Banach Spaces

analysis taylor-expansion banach-spaces normed-spaces

asked Apr 21, 2020 at 19:03

3 votes

1 answer

163 views

Are there any interesting non standard models of $Q$?

elementary-set-theory first-order-logic model-theory

asked Mar 25, 2021 at 21:13

3 votes

1 answer

79 views

Functions of finite subsets of a set

elementary-set-theory

asked May 31, 2021 at 2:34

2 votes

0 answers

94 views

Doubt on Equality Involving Cardinal Exponentiation

set-theory cardinals

asked Mar 3, 2021 at 22:13

2 votes

1 answer

42 views

substituting algebraic numbers for their conjugates in rational functions

abstract-algebra field-theory rational-functions

asked Nov 21, 2020 at 16:42

2 votes

1 answer

122 views

Cardinality of the ranks of the constructible universe

elementary-set-theory set-theory model-theory

asked Mar 12, 2021 at 17:18

2 votes

0 answers

56 views

Understanding the proof of $\mathbb{V}=\mathbb{L}\rightarrow \Diamond$

set-theory

asked May 27 at 13:39

2 votes

1 answer

98 views

A closed loop on $\mathbb{R}^2-{0}$ with a winding number of 2 or greater must intersect on at least one point

general-topology algebraic-topology

asked May 11, 2020 at 23:13

2 votes

1 answer

83 views

Is the axiom of existence sufficient to show that replacement implies comprehension?

set-theory foundations

asked Jan 14, 2020 at 14:25

2 votes

1 answer

86 views

For a set A is it always possible to find a measurable superset A* such that $\mu^(A^-A)=0$

analysis measure-theory

asked Jul 12, 2020 at 23:25

2 votes

1 answer

67 views

Topology on Reals generated by Predicates

general-topology model-theory

asked Jul 17, 2020 at 2:32

2 votes

1 answer

73 views

Proof: a group action on a $T_2$ space that is free and wandering is properly discontinuous

general-topology algebraic-topology

asked Dec 8, 2019 at 22:33

2 votes

1 answer

167 views

Proof that in a simple group of order 168 the intersection of the normalizers of two distinct 7-sylows is of order 3

abstract-algebra group-theory proof-verification sylow-theory simple-groups

asked Nov 13, 2019 at 14:03

2 votes

1 answer

63 views

Any total relation is extensional

elementary-set-theory relations

asked Jul 10, 2019 at 1:18

1 vote

2 answers

586 views

Proof for sequentially continuous function with a first countable domain is continuous

sequences-and-series general-topology continuity first-countable

asked Oct 8, 2019 at 15:01

1 vote

1 answer

108 views

Proof that a metric space $X$ isometrically embeds to the set of bounded continuous functions from $X$ to $\mathbb R$

functions metric-spaces isometry

asked Oct 10, 2019 at 15:49

1 vote

4 answers

119 views

Show $\mathbb{R}^n\setminus \{0\}$ is not homeomorphic to $\mathbb{R}^n $

real-analysis general-topology

asked Dec 6, 2019 at 23:11

1 vote

1 answer

43 views

Visualizing the fundamental group of a cylinder

general-topology homotopy-theory

asked Dec 11, 2019 at 11:11

1 vote

2 answers

32 views

Linear map $L$ from $\mathbb{R}^3$ to $\mathbb{R}^3$ such that $L^2=-Id$

linear-algebra

asked Apr 4, 2020 at 23:46

1 vote

0 answers

51 views

Proof verification of Set theory problem

elementary-set-theory solution-verification equivalence-relations

asked Jun 4 at 15:51

1 vote

0 answers

79 views

Any other norms on $\mathbb{R}^n$?

vector-spaces normed-spaces

asked Oct 23, 2020 at 1:51

1 vote

1 answer

101 views

is $\omega$ in every model of ZFC always isomorphic to the standard natural numbers

set-theory model-theory

asked Nov 8, 2020 at 14:19

1 vote

0 answers

92 views

Is there an easy way to picture a Whitney embedding?

differential-geometry differential-topology smooth-manifolds

asked Mar 11, 2021 at 15:06

0 votes

2 answers

93 views

Understanding the arc length parameter notation

differential-geometry notation arc-length

asked Jan 5, 2021 at 0:55

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36 Questions

Finding where in Ramsey's theorem one uses the Axiom of choice

Examples of Substructures that "do not know they are that substructure"

Proof that $G_\delta$ sets in $\mathbb{R}$ are either countable,finite, or have cardinality of the continuum.

If $\kappa=\kappa^{<\kappa}$ then there is a dense linear order of size $\kappa$ in which all ordinals $<\kappa^+$ can embed.

Proof that the quotient space of $\mathbb{R}^2/L$ where $L$ is a line passing through the origin is not first countable

Proof Cancellation property in lattice implies distributivity

Derivative of generalized Taylor expansion of a function between Banach Spaces

Are there any interesting non standard models of $Q$?

Functions of finite subsets of a set

Doubt on Equality Involving Cardinal Exponentiation

substituting algebraic numbers for their conjugates in rational functions

Cardinality of the ranks of the constructible universe

Understanding the proof of $\mathbb{V}=\mathbb{L}\rightarrow \Diamond$

A closed loop on $\mathbb{R}^2-{0}$ with a winding number of 2 or greater must intersect on at least one point

Is the axiom of existence sufficient to show that replacement implies comprehension?

For a set A is it always possible to find a measurable superset A* such that $\mu^(A^-A)=0$

Topology on Reals generated by Predicates

Proof: a group action on a $T_2$ space that is free and wandering is properly discontinuous

Proof that in a simple group of order 168 the intersection of the normalizers of two distinct 7-sylows is of order 3

Any total relation is extensional

Proof for sequentially continuous function with a first countable domain is continuous

Proof that a metric space $X$ isometrically embeds to the set of bounded continuous functions from $X$ to $\mathbb R$

Show $\mathbb{R}^n\setminus \{0\}$ is not homeomorphic to $\mathbb{R}^n $

Visualizing the fundamental group of a cylinder

Linear map $L$ from $\mathbb{R}^3$ to $\mathbb{R}^3$ such that $L^2=-Id$

Proof verification of Set theory problem

Any other norms on $\mathbb{R}^n$?

is $\omega$ in every model of ZFC always isomorphic to the standard natural numbers

Is there an easy way to picture a Whitney embedding?

Understanding the arc length parameter notation