Abstract algebra is the study of algebraic objects. Some of the more common algebraic objects are groups, rings, fields, vector spaces, modules, and other advanced topics.

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How do I effectively solve this kinds of problems?

I'm preparing for a test on Monday. This is an exercise in the past homework. Find all subgroups of $\mathbb{Z}_2\times \mathbb{Z}_2\times\mathbb{Z}_4$ isomorphic to $Z_2\times Z_2$. Is there a ...
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Lie bracket of vector fields on $R^2$

Compute the Lie bracket$$\Big[-y\frac{\partial}{\partial x}+x\frac{\partial}{\partial y},\frac{\partial}{\partial x}\Big]$$ on $R^2$ Can you help me please?
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The first Weyl algebra is Calabi-Yau

Why is the Weyl algebra $A_1(k)$ over a field $k$ Calabi-Yau? (My definition of Calabi-Yau is Ginzburg's)
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+50

Non simplicity of a group of order $p^{100}q$ given some conditions.

Let $G$ be a group $p$, $q$ primes $p\neq q$, $|G|=p^{100}q$. 1.- Assume that $G$ has two different $p$-Sylow subgroups and intersection for each pair of $p$-Sylow subgroups is trivial. Show that ...
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Why the rank of finitely generated finite abelian group is 0?

I haven't proven 'the fundamental theorem of finitely generated abelian group' Nevertheless, it's written in my text(Dummit,Foote - p.159) it's gonna be proven in a later chapter. Also, it's written ...
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$\mathbb{Z}/(p)^n$ does not contain a field if $n \geq 2$?

Show that $\mathbb{Z}/(p)^n$ does not contain a field if $n \geq 2$ and cannot be made into a vector space over $\mathbb{F}_p$ in a compatible way with its Abelian structure.
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Minimal polynomial: is $\sqrt[3]{2+\sqrt{5}}+\sqrt[3]{2-\sqrt{5}}=1$?

I was wondering about the minimal polynomial of real number $$u=\sqrt[3]{2+\sqrt{5}}+\sqrt[3]{2-\sqrt{5}}$$ over field $\mathbb{Q}$. As you can see here, I worked out that $u$ is a root of monic ...
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what is the definition of linearly independent subset of abelian group?

WHat is the definition of linearly independent subset of abelian group? I know the concept of this, but i don't know how to define this term precisely. Below is what i tried to formulate: Let ...
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58 views

Which non-Abelian finite groups contain the two specific centralizers? - part II

This is a question requiring the good knowledge of group theory: (Q1) Which finite groups $G$ contains some specific centralizers isomorphic to both of these two groups (but may contain other ...
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Which finite groups contain the two specific centralizers?

This is a question requiring the good knowledge of group theory: (Q1) Which finite groups $G$ contains some specific centralizers both of these two groups: i. the elementary group $Z_2^4$, ...
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Subgroup of group of order $44$

Pick the correct statement(s) below: $(a)$ There exists a group of order $44$ with a subgroup isomorphic to $ Z_2 + Z_2 $. $(b)$ There exists a group of order $44$ with a subgroup isomorphic to $ ...
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To Find a subgroup of order $6$ in $U(700).$

Find a subgroup of order $6$ in $U(700).$ Attempt: $U(700)=U(2^2.5^2.7)\thickapprox U(2^2) \oplus U(5^2)\oplus U(7)$ $\thickapprox \mathbb Z_2 \oplus \mathbb Z_{5^2-5} \oplus \mathbb Z_{7-7^0}$ ...
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normal group $(\text{ker }g)(\text{ker } f)$ as a kernel of some group using $f$ and $g$

For group homomorphism $f: A\to B$ and $g: A\to C$ we know $\text{ker }f\cap \text{ker } g$ is kernel of $(f,g): A\to B\times C$. $(\text{ker }g)(\text{ker } f)$ is trivially normal in $A$, can we ...
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Showing that a set is Discrete Valuation Ring

An order function on a field $K$ is a function $ϕ:K→Z∪{∞}$ satisfying: i) $ϕ(a)=∞$ if and only if $a=0$. ii) $ϕ(ab)=ϕ(a)+ϕ(b)$. iii) $ϕ(a+b)≥min(ϕ(a),ϕ(b))$. Show that R=$\{z∈K∣ϕ(z)≥0\}$ is a DVR ...
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Subfield of the Galois Group of $x^5 - 1$

Why is it that the subfield fixed by the subgroup of this Galois group is $\mathbb{Q}(\sqrt5)$. Can someone explain it without using the cyclotomic extension of $\mathbb{Q}$? Thank you edit: Using ...
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Separable and Splitting fields

Does a separable field imply splitting field? I am thinking yes. For $F < E$ If every $\alpha \in E$ is separable over $F$ then it must be that $E$ is a $S.F.$ over $F$? Also we have the ...
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Sub-modules of free modules

I'm going back through basic module theory notes, and I've come across a paragraph explaining that a sub-module of a finitely generated free module may not itself be free. In my course a free module ...
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Ring of fractions $S^{-1}A$ and localisation

I'd really appreciate if somebody could help me with the problem 6.4 Reid (Undergraduate commutative algebra), because I've been trying to get the solutions for days and I don't see it. (a) Give an ...
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If $A \in M_{n,n}(\mathbb F)$ is invertible then $A = UPB$, $U$ is unipotent upper triangular, $B$ is upper triangular and $P$ is a permutation.

If $A \in M_{n,n}(\mathbb F)$ is invertible then $A = UPB$, where $U$ is unipotent upper triangular, $B$ is upper triangular and $P$ a permutation matrix. A hint is given that one could relate ...
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Is this type of a subgroup always normal? [duplicate]

Let $G$ be a finite group, and let $H$ be a subgroup of $G$ such that the index $(G\colon H)$ of $H$ in $G$ is the smallest prime that divides the order of $G$. Can we say anything about whether or ...
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1answer
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Obtaining representations of $G$ from $\mathrm{Lie}(G)$.

Suppose $\mathfrak{g}$ is a semisimple Lie algebra over $\mathbb{C}$, and $\tilde{G}$ is the unique connected, simply connected Lie group whose Lie algebra is $\mathfrak{g}$. Let $C$ be any discrete ...
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When proving a partial order relation is a total order do we have assume both elements are distinct?

Consider the "divides" relation on the set $A=\lbrace 1,2,2^2,.\;.\;.,2^n\rbrace$, where $n$ is a non-negative integer. Prove that this relation is a total order on $A$. First we prove $A$ is a ...
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Need an explanation for homomorphism in commutative algebra

I'm self-learning commutative algebra following "Introduction to Commutative Algebra". When dealing with concepts like "contraction" and "extension", some exercises in this book don't specify which ...
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If G/Z(G) is abelian, then H/Z(H) is also abelian.

Let H be a subgroup of G. If G/Z(G) is abelian, then H/Z(H) is also abelian. I am trying to prove this property yet I don't know how I should proceed. Any help? Thank you.
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Proof about dual bases?

Let V be a finite dimensional vector space over a field F. Let B={v1,v2, ..., vn} be a basis and consider the dual basis B*={v1*,v2*,...,vn*}. Let a be an element of V*. prove that $$v = ...
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24 views

Do disjoint cycles commute?

When a given set is finite it is clear. I'm asking the general case. Let $X$ is an arbitrary set. Let $\sigma,\tau$ be disjoint cycles on $X$. Then do they commute?
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25 views

Direct Products Help Abstract

Let Z be the additive group of integers and S = {-1,1} be a group under multiplication. Is the product Z x S cyclic? Why or why not? I am really confused on this question and have no idea where to ...
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Abstract Direct Product Proof Help

Let G = G1 x G2. Let H = {(x1, e2) : x1 ∈ G1} and K = {(e1, x2) : x2 ∈ G2}. (a) Prove H ≤ G and K ≤ G. (b) Prove that HK = KH = G (c) Prove that H ∩ K = {(e1, e2)} (d) Show that G/H is isomorphic to ...
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proving a natural projection is linear and finding its kernel

Let $V_i = 1,...,N$ be a collection of vector spaces over a field $F$. Consider the Cartesian product $V=V_1 \times V_2 \times ... \times V_N$ with the natural projections $\pi=V \rightarrow V_i$. ...
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In algebraic extension, field homomorphism induces isomorphism.

I read this page's first answer. But I'm curious about why $\varphi$ induces injective map $S \to S$. Isn't it possible to make $\varphi(\alpha)= k$ such that $k$ is not root of $f(X)$?
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Canonically isomorphic but not equal

In mathematics, we have many objects that are canonically isomorphic but not equal on the nose. For example let $V$ and $W$ be vector spaces. Then $V\otimes W$ and $W\otimes V$ are canonically ...
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Equivalence Relations and distinct equivalence classes

$A=\lbrace(1,3),(2,4),(-4,-8),(3,9),(1,5),(3,6)\rbrace$. $R$ is defined on $A$ as follows: For all $(a, b)\;(c, d) \in A$, $(a, b) R (c, d) \iff ad=bc$ I know what they are asking but I cannot see ...
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A construction of $\mathfrak{e}_8$ in Fulton and Harris

In section $22.4$ of "Representation Theory: A First Course" by Fulton and Harris, the exceptional Lie algebra $\mathfrak{e}_8$ is constructed using a method of Freudenthal. For background, I will ...
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Tensoring over a direct sum of R

Is tensoring over a ring R same as tensoring over a finite direct sum of R. I mean is $A \otimes_R B$ isomorphic to $A \otimes_{R^n} B$? And if it doesnt hold for any ring $R$, Does it hold for ...
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What is the definition of “disjoint cycles”?

I'm the one who thinks clear definition(clear with meta-language) is very important for doing mathematics. Below, i list my definitions for cycle and orbit. Let $X$ be a nonempty set. Let ...
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If G is a finite group and $x \in G$, there is an integer n $\geq 1$ such that $x^n = e$

Let G be a finite group. Show that, given $x \in G$, there is an integer n $\geq 1$ such that $x^n = e$. I'm trying to use the info that is finite, but I can't find a way. For instance, if G is a ...
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Under what conditions on the field k will all symmetric matrices be diagonalizable?

It's a theorem that if $A$ is an $n \times n$ symmetric matrix ($A = A^{T}$) with real entries, then $A$ is diagonalizable. The proof goes like this: $A$ has a complex eigenvalue, since $\mathbb{C}$ ...
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Direct Products Helps Abstract

Classify the group (Z4 x Z2)/({0} x Z2). I know the order of (Z4 x Z2)/({0} x Z2) is 4, and groups with order 4 are either the Klein-4 Group or Z4. I know Z4 is abelian and cyclic and the Klein-4 ...
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What are the finite groups with 8 or 16 conjugacy classes?

What are the list of finite groups with 8 or 16 conjugacy classes? I learned that dihedral groups $D_{10}$ and $D_{13}$ have 8 conjugacy classes. (Here the order of these groups are $|D_{10}|=20$, ...
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An application of Sylow theorems in p-groups!

If $G$ is a finite group of order $p^{n}$ (which $p$ is a prime number) and have only one subgroup of order $p^{n-1}$ ,namely $H$ ,then $G$ is cyclic ! My "proof" is as follows: suppose $$x\in G-H$$ ...
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Why is the method to finding the order of a torsion subgroup different than finding the maximum order of a given element of a direct product?

If we want to find the maximum order of a given element of say $\mathbb{Z}_3\times \mathbb{Z}_4$. We would have $lcm{(3,4)}=12$ is the maximum order. But if we take a look at finding the order of the ...
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The form of subrings of $k[[t]]$

I saw this question in an algebraic geometry book. I tried to solve this. But I did trivial thing, so I don't write what I did here. This is just self-studying. I want to learn how to solve. Please ...
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Lower bound of the index of a subgroup of a non abelian simple group

Let $G$ be a simple , non abelian group . Let $H$ be a subgroup of $G$ such that $[G:H] < \infty$ . Show that: $[G:H] \ge 5$
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Necessary and sufficient conditions for $\rm P \neq NP$ maybe?

Please review the $\rm P \neq NP$ problem here. I'm working on an algebraic approach to this problem, and all my notes are currently here. Conjecture 1 For all $f \in F[x_1, \dots, x_k]$, a minimal ...
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Derived subgroup of the base group of a standard wreath product

Let $G=H\wr K$ be the standard wreath product with $K\ne 1$. Prove that $B'\leq [B,K]$ where $B$ is the base group of $G$. Deduce that $G/[B,K]\cong (H/H')\times K$. This is problem 1.6.20 from ...
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What is “the orbit of a permutation”? Is the term “orbit” consistent with that for group action?

reference: What is the orbit of a permutation? To be honest, i don't understand the answer in the link. The orbit of a group action is defined as follows: Let $G$ be a group acting on a set $X$. ...
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Is there some kind of right distributivity of the subset predicate over set union?

$X \cup Y \subset Z \leftrightarrow X \subset Z \wedge Y \subset Z$. Is there a similar simple rule for $X \subset Y \cup Z$?
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What's the point of defining left ideals?

I admit, I haven't gotten really far in studying abstract algebra, but I was always curious (ever since I saw a definition of an ideal) why is the notion of left-sided ideal introduced when we ...
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How to solve this boolean algebra problem?

Given two expressions: $$A\bar{D}+A\bar{C}D +A\bar{B}C + ABCD = Y$$ and $$BD+A\bar{C}D=Z$$ is there a way to simplify this using the rules for Boolean Algebra? I tried different combinations, but if I ...
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Can covering be done on two elements?

The covering rule is: $$B \bullet (B+C) = B$$ and $$B+(B \bullet C)=B$$ So does it follow from this rule that: $$B \bullet A \bullet \bar{C} + B \bullet D \bullet\bar{F} = B \bullet ...