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Let $|G|$ be infinite. Use normal cores (not Poincaré's Theorem) to prove that if $H, K$ have finite index in $G$, then so does $H\cap K$.

group-theory group-actions normal-subgroups infinite-groups

asked 2 mins ago Shaun 27.4k

0

votes

3

answers

9

views

Limit point clarification

general-topology advice

answered 3 mins ago mrsamy 4,958

0

votes

1

answer

14

views

CDF and PDF of non-monotonic transformations

statistics transformation

answered 3 mins ago gogurt 1,944

0

votes

0

answers

5

views

Find all units, zero divisors and nilpotent elements of $\mathbb{Z}_4[X]$ and $\mathbb{Z}_6[X]$

abstract-algebra polynomials ring-theory integers nilpotence

asked 4 mins ago Alejandro Bergasa Alonso 2,080

-1

votes

0

answers

4

views

How can we prove the correctness of the integration property of the Laplace transform?

laplace-transform signal-processing

asked 5 mins ago Aditya S 1

2

votes

1

answer

19

views

A question about two rules in isomorphism and cardinality

elementary-set-theory set-theory

modified 7 mins ago Hagen von Eitzen 337k

1

vote

0

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17

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$\lim_{n \to \infty}\int_0^1x^nf(x)d \mu =0$

analysis lebesgue-measure

asked 7 mins ago Frederick Manfred 379

0

votes

0

answers

4

views

Harmonic functions $u$ and $v$ such that $\nabla u = a \nabla v$ for some function $a$.

harmonic-functions

asked 8 mins ago Nikola Ubavić 557

0

votes

0

answers

9

views

Exercise 2.13 Atiyah-Macdonald Introduction to commutative algebra

solution-verification modules tensor-products

asked 10 mins ago love_sodam 623

0

votes

0

answers

20

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Can a Banach limit be invariant to any rearrangment of the argument?

real-analysis functional-analysis limits lp-spaces hahn-banach-theorem

modified 10 mins ago Ban 395

0

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0

answers

7

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Does the difference between a subset and a measurable cover thereof have outer measure $0$?

measure-theory outer-measure

modified 11 mins ago Evan Aad 9,478

1

vote

0

answers

36

views

Does Euclidean metric imply the space is flat?

geometry reference-request soft-question

modified 13 mins ago Julien Pitteloud 143

10

votes

0

answers

23

views

Why does plotting Collatz sequences in polar coordinates produce a cardioid and nephroid?

number-theory polar-coordinates collatz-conjecture

modified 16 mins ago Kyle Giddon 101

0

votes

1

answer

18

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Epsilon-N method: proving recursive sequence

sequences-and-series convergence-divergence solution-verification

modified 16 mins ago jje 1

1

vote

1

answer

45

views

How to solve this integral on the unit interval

calculus integration indefinite-integrals

modified 17 mins ago Quanto 48.9k

1

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1

answer

23

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Submodularity of objective function

measure-theory optimization robotics

answered 17 mins ago Gantavya Bhatt 11

0

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1

answer

12

views

What morphisms must exist in a category if the morphism between two hom-sets relative to that category's objects exist?

category-theory morphism

answered 18 mins ago Alex Kruckman 46.5k

0

votes

0

answers

11

views

Approximate (continuous) functions by step functions - Convergence Rate

functional-analysis numerical-methods approximation approximation-theory

asked 19 mins ago Hari.M.S. 89

0

votes

0

answers

6

views

Is the map $\ g:S \otimes_R A \to T \otimes_R A \ $ also faithfully flat?

commutative-algebra tensor-products

modified 19 mins ago Masmath 492

0

votes

0

answers

27

views

Proof of Lagrange multipliers for holonomic constraints

calculus analysis optimization calculus-of-variations lagrange-multiplier

modified 20 mins ago userr777 674

6

votes

1

answer

76

views

How to integrate $\int_{0}^{2\pi}\cos x\times \exp\left [ \frac{a}{\cos x}\right]\,dx$

complex-analysis definite-integrals complex-integration

modified 29 mins ago metamorphy 21.8k

0

votes

1

answer

17

views

Comparing the size of the sets

set-theory

answered 31 mins ago Eduardo Magalhães 2,143

0

votes

0

answers

11

views

$\lim_{n\to\infty}n^{2020}\int^{\pi/2}_0 (\sin x)^n * (\pi/2-x)^n\,dx $

integration limits definite-integrals

modified 32 mins ago Bernard 162k

0

votes

1

answer

10

views

Interactions (MIMO systems)

control-theory

answered 32 mins ago SampleTime 2,214

0

votes

1

answer

26

views

${\{n\sqrt{2}\}>\frac{1}{2n\sqrt{2}}}$ for all $n\in \mathbb{N}^*$

inequality ceiling-and-floor-functions

modified 33 mins ago GNUSupporter 8964民主女神地下教會 16.8k

1

vote

1

answer

49

views

one point sets are open as a topology

general-topology

modified 40 mins ago Henno Brandsma 185k

0

votes

1

answer

24

views

Verify $f: \mathbb{Z} ⟶ \mathbb{Z}_{r} \times \mathbb{Z}_{s}$ given by $a ⟶ (ā_r, ā_s)$ is an epimorphism

abstract-algebra ring-theory ring-homomorphism

answered 44 mins ago Carlo 3,796

0

votes

1

answer

23

views

Applying Gaus formula to find flux

integration divergence-theorem

modified 45 mins ago Felix Marin 81.1k

1

vote

0

answers

22

views

Finding seven harmonic cubics

algebraic-geometry computational-geometry laplacian computational-algebra homogeneous-spaces

modified 46 mins ago B.K-Theory 323

3

votes

0

answers

269

views

Grothendieck's schematic point of view of regular polyhedra

geometry reference-request polyhedra

modified 47 mins ago RavenclawPrefect 6,015

0

votes

0

answers

8

views

Second moment of Silverman kernel

integration definite-integrals density-function moment-problem

asked 50 mins ago PaulWH 87

0

votes

1

answer

12

views

arbitrary product of the closed unit interval is Hausdorff

general-topology

answered 52 mins ago Henno Brandsma 185k

0

votes

0

answers

28

views

What is the ratio between 100 and 0? 100? undefined?

percentages ratio

modified 53 mins ago N. F. Taussig 58.5k

1

vote

0

answers

14

views

Show that this set is convex

real-analysis general-topology convex-analysis normed-spaces

asked 53 mins ago Alphie 1,035

0

votes

1

answer

31

views

The product of a number and the largest integer smaller than the same number is $11$. …

algebra-precalculus

answered 54 mins ago user2661923 6,883

0

votes

1

answer

36

views

Notation for multilinear maps - is there a good reason why it is not common to write $\text{ML}(V_1\times\ldots\times V_n,W)$?

linear-transformations multilinear-algebra convention

modified 59 mins ago Filippo 733

2

votes

0

answers

22

views

On a limit of permutation groups

group-theory permutations

asked 1 hour ago RB1995 75

0

votes

0

answers

2

views

Simplification of sum and average (2SLS)

regression economics causality

asked 1 hour ago randomname 87

3

votes

1

answer

227

views

Numbers on clock represented by polyhedra

geometry sequences-and-series polyhedra

answered 1 hour ago RavenclawPrefect 6,015

0

votes

1

answer

24

views

Finding eigenvalues of block type matrix

linear-algebra matrices eigenvalues-eigenvectors symmetric-matrices block-matrices

modified 1 hour ago Zalnd 446

2

votes

0

answers

20

views

Prove certain polynomials are irreducible in $\mathbb{Q}[X]$

abstract-algebra polynomials ring-theory irreducible-polynomials rational-numbers

modified 1 hour ago Alejandro Bergasa Alonso 2,080

1

vote

1

answer

67

views

Prove that there are infinitely positive integer $n$ satisfy $\left(\lfloor \sqrt{n} \rfloor+\lfloor \sqrt{\tfrac{n}{2}}\rfloor\right)\mid n$

number-theory divisibility

answered 1 hour ago sirous 4,719

1

vote

1

answer

26

views

Simplification in the curvature tensor identity

differential-geometry

modified 1 hour ago lulu 2,613

11

votes

0

answers

61

views

Does there exist a real function with following properties?

real-analysis calculus

modified 1 hour ago N.Quy 932

0

votes

1

answer

27

views

There are pairs of rational numbers $(a,b)$

integration definite-integrals rational-numbers

answered 1 hour ago Raffaele 23.3k

0

votes

0

answers

7

views

Property of transpose Tr in category of modules (Auslander-Reiten theory)

representation-theory homological-algebra

asked 1 hour ago Ji Woong Park 68

2

votes

3

answers

47

views

Conic equation: ${4x^{2}−4xy+7y^{2}+12x+6y−9=0}$ Converting this conic to “standard form”

analytic-geometry conic-sections elliptic-equations

modified 1 hour ago Quanto 48.9k

1

vote

2

answers

930

views

Pizza-topping problem with 8 slices, 10 toppings and constraints

combinatorics

modified 1 hour ago Community♦ 1

1

vote

1

answer

14

views

Gradience wrt a Position Vector

vector-analysis

modified 1 hour ago Svyatoslav 456

4

votes

1

answer

45

views

Obtain B to minimize $\|\boldsymbol{X}-\boldsymbol{B}\|_{\boldsymbol{F}}^{2}$ with constraint on the spectral norm of B to be ≤ 1

matrices optimization svd matrix-norms

modified 1 hour ago Stacker 855

0

votes

0

answers

15

views

Prove that joint distribution of mutiple i.i.d categorical variables is a multinomial distribution

probability probability-distributions proof-writing

modified 1 hour ago Guest1 11

3

votes

1

answer

158

views

If I chop my apple into smaller pieces, can I fit more apple in my lunchbox?

geometry packing-problem

answered 1 hour ago RavenclawPrefect 6,015

0

votes

1

answer

14

views

How can i calculate the contour integral of this trigonometric function?

contour-integration complex-integration trigonometric-integrals

modified 1 hour ago Turing 21.7k

0

votes

0

answers

24

views

A direct formula for counting 1s in binary form of a positive integer

number-theory binary binary-operations

modified 1 hour ago user0410 548

0

votes

0

answers

7

views

How big are periods in PCG?

algorithmic-randomness

modified 1 hour ago Tom 29

0

votes

5

answers

31

views

If $X$ is a set, what does $S(X) = \{f\colon X \to X | \text{where f is a bijection}\}$ mean?

group-theory functions elementary-set-theory automorphism-group

answered 1 hour ago user 280

9

votes

3

answers

5k

views

What are the least sets of generators for $S_n$

group-theory finite-groups symmetric-groups

answered 1 hour ago 27182818284tropy 75

1

vote

0

answers

20

views

How to find a tessellation from a basis of linear transformations?

linear-algebra symmetry coxeter-groups tessellations

modified 1 hour ago PaulC 11

4

votes

1

answer

172

views

Relation between Stirling numbers of first kind and harmonic numbers

sequences-and-series harmonic-numbers stirling-numbers

modified 1 hour ago metamorphy 21.8k

0

votes

0

answers

19

views

Dirichlet L functions

number-theory power-series riemann-zeta dirichlet-series

asked 1 hour ago Mr. N 278

9

votes

1

answer

69

views

What are all the integral solutions of $n!=m(m^2-1)$?

number-theory elementary-number-theory arithmetic diophantine-equations integers

answered 1 hour ago Favst 2,727

0

votes

1

answer

9

views

Kolmogorov Differential Equations governing random dynamical system

stochastic-processes stochastic-calculus

answered 1 hour ago caverac 17.2k

1

vote

1

answer

17

views

Banach spaces admitting a coarser topology for which the closed unit ball is compact.

functional-analysis banach-spaces locally-convex-spaces weak-topology reflexive-space

answered 1 hour ago GEdgar 83.1k

0

votes

0

answers

21

views

How to find a polynomial that passes through a set of points (not just 1)?

algebra-precalculus

asked 1 hour ago visualbread 63

2

votes

0

answers

19

views

Determine the ray pair at the origin of a vein in the Mandelbrot set.

complex-dynamics

modified 1 hour ago Claude 3,918

1

vote

1

answer

29

views

Does $\int_{I}f(t)g(t)dt = 0$ for every $g|_{\partial I} = 0$ implies $f\equiv 0$?

real-analysis analysis

answered 1 hour ago TSU 448

1

vote

0

answers

12

views

Induced automorphism on $\pi_1(S,x)$ from push map $\pi_1(S,x)\to\text{Mod}(S,x)$ is an inner automorphism

geometric-topology mapping-class-group

asked 1 hour ago Katherine 231

0

votes

0

answers

32

views

Hints to prove $\int_0^\infty g(t)f(t)dt=0$ for $g$ continuous and compact support, $\mathcal{L}(f)(n)=0$

laplace-transform

modified 1 hour ago Valerin 1,861

1

vote

1

answer

22

views

Stuck in a case of proving that $L_1$ is complete

logic propositional-calculus

answered 2 hours ago Rob Arthan 35.2k

0

votes

0

answers

11

views

Find the unitary operator responsible for finite translation in time.

calculus linear-algebra quantum-mechanics

asked 2 hours ago LSS 105

0

votes

0

answers

16

views

Why can I change the sign of this expression?

linear-algebra

asked 2 hours ago Toast 1

0

votes

0

answers

14

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Propositional Resolution

logic propositional-calculus

modified 2 hours ago Mauro ALLEGRANZA 82.8k

1

vote

0

answers

23

views

Tree-width and Maximum Cliques of Triangulation - Confusion over proof.

graph-theory trees

modified 2 hours ago t-tough 441

1

vote

1

answer

19

views

Compact-open topology for the space of continuous paths

general-topology algebraic-topology

answered 2 hours ago Sam Freedman 1,767

0

votes

0

answers

9

views

Interesting inequality in R3 about number of lines with given angle between them

linear-algebra geometry

asked 2 hours ago KhaBeleth 83

1

vote

0

answers

9

views

Computability of Convergence

sequences-and-series convergence-divergence computability

asked 2 hours ago Derive Foiler 323

1

vote

1

answer

29

views

Conditional Markov Chain

probability-theory probability-distributions markov-chains

modified 2 hours ago Jeroen van der Meer 470

0

votes

0

answers

12

views

How to express symmetric polynomials in terms of elementary symmetric polynomials?

abstract-algebra symmetric-polynomials symmetric-functions

asked 2 hours ago Verza Jr. 323

0

votes

0

answers

12

views

Integrating a function in spherical polar coordinates

integration polar-coordinates spherical-coordinates

asked 2 hours ago abhi 1

1

vote

0

answers

7

views

Calculating the distance between two objects with known heights in an image in which forced perspective appears to make them the same height?

measure-theory trigonometry equivalence-relations projective-geometry equivalent-metrics

asked 2 hours ago NerdyDeeds 11

1

vote

0

answers

7

views

SEIR model with births and deaths - plot phase plane with Maple

maple

modified 2 hours ago zarate 11

7

votes

0

answers

27

views

A question about S4 modal system

logic

modified 2 hours ago ferdinand 480

2

votes

2

answers

28

views

Bijection between a set of injections and a union of bijection

elementary-set-theory

answered 2 hours ago Christoph 20k

0

votes

1

answer

17

views

Time-invariance of a MIMO system

control-theory

answered 2 hours ago Petrus1904 241

5

votes

0

answers

36

views

How many combinatorially distinct ways are there to tile an equilateral triangle with $k$ $60^\circ-120^\circ$ trapezoids?

geometry reference-request tiling oeis

modified 2 hours ago RavenclawPrefect 6,015

0

votes

0

answers

12

views

Check if $X$ is completely metrizable

general-topology complete-spaces metrizability

asked 2 hours ago dsk62 155

0

votes

0

answers

11

views

Trigonometry Quadrants: Cosine of angle in the third quadrant

trigonometry

asked 3 hours ago mku 103

1

vote

1

answer

20

views

How does $ 0 \le a \lt p^\alpha $ in Theorem 5.30 of Introduction to Analytic Number Theory (Apostol)?

number-theory inequality modular-arithmetic

answered 3 hours ago Andrea Marino 2,766

0

votes

2

answers

27

views

Taylor expansion in complex analysis. Why $f(z)=\operatorname{Log} (z+1)$?

complex-analysis taylor-expansion

answered 3 hours ago Bernard 162k

0

votes

1

answer

43

views

Chapter 1.3 Proposition 3.5 of Robin Hartshorne's Algebraic geometry.

algebraic-geometry affine-varieties continuous-homomorphisms

answered 3 hours ago Jeroen van der Meer 470

3

votes

2

answers

76

views

Vectors in Physics vs. Vectors in Abstract Linear Algebra

linear-algebra vector-spaces physics classical-mechanics

answered 3 hours ago Paul Frost 39.1k

1

vote

0

answers

16

views

Boundaries in Spaces where Quasicomponents and Components Coincide

general-topology compactness connectedness locally-connected continuum-theory

modified 3 hours ago John Samples 1,391

2

votes

0

answers

12

views

Law of large numbers for weakly correlated Gaussian random variables

probability probability-theory measure-theory normal-distribution law-of-large-numbers

asked 3 hours ago mark 493

1

vote

0

answers

5

views

Make the link between Generalized eigenvecors and MLE to buid a cross-correlated Fisher or Covariance matrix in order to get better constraints

eigenvalues-eigenvectors covariance estimation maximum-likelihood fisher-information

asked 3 hours ago youpilat13 55

5

votes

0

answers

53

views

Solve $x^3=(1256)(37)$ in $S_7$

abstract-algebra group-theory permutations symmetric-groups

modified 4 hours ago Shaun 27.4k

3

votes

1

answer

23

views

Is the set of essentially bounded non-measurable functions a Banach space?

functional-analysis measure-theory

answered 4 hours ago Ruy 7,200

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