diff options
| author | Juan Marin Noguera <juan@mnpi.eu> | 2022-12-31 13:13:32 +0100 |
|---|---|---|
| committer | Juan Marin Noguera <juan@mnpi.eu> | 2022-12-31 13:13:32 +0100 |
| commit | de3e935e35f0fdad86aaf142e657cd9c0fbf0ef8 (patch) | |
| tree | 0e8b1a3733ac53b621f6b8e59c0ec771bb85de4a /ac/na.lyx | |
| parent | c4f1b931887d96b91f7c984479203ad20ed80b54 (diff) | |
Terminados apuntes de Álgebra Conmutativa
Diffstat (limited to 'ac/na.lyx')
| -rw-r--r-- | ac/na.lyx | 1250 |
1 files changed, 1250 insertions, 0 deletions
diff --git a/ac/na.lyx b/ac/na.lyx new file mode 100644 index 0000000..1f36678 --- /dev/null +++ b/ac/na.lyx @@ -0,0 +1,1250 @@ +#LyX 2.3 created this file. For more info see http://www.lyx.org/ +\lyxformat 544 +\begin_document +\begin_header +\save_transient_properties true +\origin unavailable +\textclass book +\begin_preamble +\input{../defs} +\end_preamble +\use_default_options true +\maintain_unincluded_children false +\language spanish +\language_package default +\inputencoding auto +\fontencoding global +\font_roman "default" "default" +\font_sans "default" "default" +\font_typewriter "default" "default" +\font_math "auto" "auto" +\font_default_family default +\use_non_tex_fonts false +\font_sc false +\font_osf false +\font_sf_scale 100 100 +\font_tt_scale 100 100 +\use_microtype false +\use_dash_ligatures true +\graphics default +\default_output_format default +\output_sync 0 +\bibtex_command default +\index_command default +\paperfontsize default +\spacing single +\use_hyperref false +\papersize default +\use_geometry false +\use_package amsmath 1 +\use_package amssymb 1 +\use_package cancel 1 +\use_package esint 1 +\use_package mathdots 1 +\use_package mathtools 1 +\use_package mhchem 1 +\use_package stackrel 1 +\use_package stmaryrd 1 +\use_package undertilde 1 +\cite_engine basic +\cite_engine_type default +\biblio_style plain +\use_bibtopic false +\use_indices false +\paperorientation portrait +\suppress_date false +\justification true +\use_refstyle 1 +\use_minted 0 +\index Index +\shortcut idx +\color #008000 +\end_index +\secnumdepth 3 +\tocdepth 3 +\paragraph_separation indent +\paragraph_indentation default +\is_math_indent 0 +\math_numbering_side default +\quotes_style french +\dynamic_quotes 0 +\papercolumns 1 +\papersides 1 +\paperpagestyle default +\tracking_changes false +\output_changes false +\html_math_output 0 +\html_css_as_file 0 +\html_be_strict false +\end_header + +\begin_body + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +begin{reminder}{GyA} +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +Llamamos +\series bold +orden +\series default + de [un grupo] +\begin_inset Formula $G$ +\end_inset + + al cardinal del conjunto. + [...] +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $A$ +\end_inset + + es un anillo, +\begin_inset Formula $(A,+)$ +\end_inset + + es su +\series bold +grupo aditivo +\series default +, que es abeliano, y +\begin_inset Formula $(A^{*},\cdot)$ +\end_inset + + es su +\series bold +grupo de unidades +\series default +, que es abeliano cuando el anillo es conmutativo. + [...] +\end_layout + +\begin_layout Standard +Llamamos +\series bold +orden +\series default + de +\begin_inset Formula $a\in G$ +\end_inset + + al orden de +\begin_inset Formula $\langle a\rangle$ +\end_inset + +, +\begin_inset Formula $|a|\coloneqq|\langle a\rangle|$ +\end_inset + +, y escribimos +\begin_inset Formula $\langle a\rangle_{n}$ +\end_inset + + para referirnos a +\begin_inset Formula $\langle a\rangle$ +\end_inset + + indicando que tiene orden +\begin_inset Formula $n$ +\end_inset + +. + El orden de +\begin_inset Formula $a$ +\end_inset + + divide al de +\begin_inset Formula $G$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Sea +\begin_inset Formula $f:\mathbb{Z}\to G$ +\end_inset + + el homomorfismo dado por +\begin_inset Formula $f(n)\coloneqq a^{n}$ +\end_inset + +, +\begin_inset Formula $\ker f=n\mathbb{Z}$ +\end_inset + + para algún +\begin_inset Formula $n\geq0$ +\end_inset + +. + Si +\begin_inset Formula $n=0$ +\end_inset + +, +\begin_inset Formula $f$ +\end_inset + + es inyectivo y +\begin_inset Formula $(\mathbb{Z},+)\cong\langle a\rangle$ +\end_inset + +, y en otro caso +\begin_inset Formula $\mathbb{Z}_{n}\cong\langle a\rangle$ +\end_inset + +, con lo que +\begin_inset Formula $n=|a|$ +\end_inset + + y +\begin_inset Formula $a^{n}=1\iff|a|\mid n$ +\end_inset + +. + De aquí, +\begin_inset Formula $a^{k}=a^{l}\iff k\equiv l\bmod n$ +\end_inset + +, con lo que +\begin_inset Formula $|a|$ +\end_inset + + es el menor entero positivo con +\begin_inset Formula $a^{n}=1$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $a$ +\end_inset + + tiene orden finito y +\begin_inset Formula $n>0$ +\end_inset + +, +\begin_inset Formula +\[ +|a^{n}|=\frac{|a|}{\text{mcd}\{|a|,n\}}. +\] + +\end_inset + +Si +\begin_inset Formula $G=\langle a\rangle$ +\end_inset + +: +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $G$ +\end_inset + + tiene orden infinito, +\begin_inset Formula $G\cong(\mathbb{Z},+)\cong C_{\infty}$ +\end_inset + + y los subgrupos de +\begin_inset Formula $G$ +\end_inset + + son los +\begin_inset Formula $\langle a^{n}\rangle$ +\end_inset + + con +\begin_inset Formula $n\in\mathbb{N}$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $|G|=n$ +\end_inset + +, +\begin_inset Formula $G\cong(\mathbb{Z}_{n},+)\cong C_{n}$ +\end_inset + + y los subgrupos de +\begin_inset Formula $G$ +\end_inset + + son exactamente uno de orden +\begin_inset Formula $d$ +\end_inset + + por cada +\begin_inset Formula $d\mid n$ +\end_inset + +, +\begin_inset Formula $\langle a^{n/d}\rangle_{d}$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Todos los subgrupos y grupos cociente de +\begin_inset Formula $G$ +\end_inset + + son cíclicos. +\end_layout + +\begin_layout Standard +Así, si +\begin_inset Formula $p\in\mathbb{N}$ +\end_inset + + es primo, todos los grupos de orden +\begin_inset Formula $p$ +\end_inset + + son isomorfos a +\begin_inset Formula $(\mathbb{Z}_{p},+)$ +\end_inset + +. + Si +\begin_inset Formula $G=\langle g_{1},\dots,g_{n}\rangle$ +\end_inset + + y +\begin_inset Formula $N\unlhd G$ +\end_inset + +, +\begin_inset Formula $G/N=\langle g_{1}N,\dots,g_{n}N\rangle$ +\end_inset + +. +\end_layout + +\begin_layout Standard + +\series bold +Teorema chino de los restos para grupos: +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $G$ +\end_inset + + y +\begin_inset Formula $H$ +\end_inset + + son subgrupos cíclicos de órdenes respectivos +\begin_inset Formula $n$ +\end_inset + + y +\begin_inset Formula $m$ +\end_inset + +, +\begin_inset Formula $G\times H$ +\end_inset + + es cíclico si y sólo si +\begin_inset Formula $n$ +\end_inset + + y +\begin_inset Formula $m$ +\end_inset + + son coprimos. + [...] +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $g,h\in G$ +\end_inset + + tienen órdenes respectivos +\begin_inset Formula $n$ +\end_inset + + y +\begin_inset Formula $m$ +\end_inset + + coprimos y +\begin_inset Formula $gh=hg$ +\end_inset + +, entonces +\begin_inset Formula $\langle g,h\rangle$ +\end_inset + + es cíclico de orden +\begin_inset Formula $nm$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Standard +Dados un grupo +\begin_inset Formula $G$ +\end_inset + + y +\begin_inset Formula $a\in G$ +\end_inset + +, llamamos +\series bold +conjugado +\series default + de +\begin_inset Formula $g\in G$ +\end_inset + + por +\begin_inset Formula $a$ +\end_inset + + a +\begin_inset Formula $g^{a}\coloneqq a^{-1}ga$ +\end_inset + +, y conjugado de +\begin_inset Formula $X\subseteq G$ +\end_inset + + por +\begin_inset Formula $a$ +\end_inset + + a +\begin_inset Formula $X^{a}\coloneqq\{x^{a}\}_{x\in X}$ +\end_inset + +. + Dos elementos +\begin_inset Formula $x,y\in G$ +\end_inset + + o conjuntos +\begin_inset Formula $x,y\subseteq G$ +\end_inset + + son +\series bold +conjugados +\series default + en +\begin_inset Formula $G$ +\end_inset + + si existe +\begin_inset Formula $a\in G$ +\end_inset + + con +\begin_inset Formula $x^{a}=y$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $a\in G$ +\end_inset + +, llamamos +\series bold +automorfismo interno +\series default + definido por +\begin_inset Formula $a$ +\end_inset + + al automorfismo +\begin_inset Formula $\iota_{a}:G\to G$ +\end_inset + + dado por +\begin_inset Formula $\iota_{a}(x)\coloneqq x^{a}$ +\end_inset + +. + Su inverso es +\begin_inset Formula $\iota_{a^{-1}}$ +\end_inset + +. + El conjugado por +\begin_inset Formula $a$ +\end_inset + + de un subgrupo de +\begin_inset Formula $G$ +\end_inset + + es otro subgrupo de +\begin_inset Formula $G$ +\end_inset + + del mismo orden. + [...] +\end_layout + +\begin_layout Standard +\begin_inset Formula $\forall g,a,b\in G,g^{ab}=(g^{a})^{b}$ +\end_inset + +, y [...] la relación de ser conjugados es de equivalencia. + Las clases de equivalencia se llaman +\series bold +clases de conjugación +\series default + de +\begin_inset Formula $G$ +\end_inset + +, y llamamos +\begin_inset Formula $a^{G}\coloneqq[a]=\{a^{g}\}_{g\in G}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Sea +\begin_inset Formula $X$ +\end_inset + + un conjunto. + Una +\series bold +acción por la izquierda +\series default + de +\begin_inset Formula $G$ +\end_inset + + en +\begin_inset Formula $X$ +\end_inset + + es una función +\begin_inset Formula $\cdot:G\times X\to X$ +\end_inset + + tal que +\begin_inset Formula $\forall x\in X,(\forall g,h\in G,(gh)\cdot x=g\cdot(h\cdot x)\land1\cdot x=x)$ +\end_inset + +, y una +\series bold +acción por la derecha +\series default + de +\begin_inset Formula $G$ +\end_inset + + en +\begin_inset Formula $X$ +\end_inset + + es una función +\begin_inset Formula $\cdot:X\times G\to X$ +\end_inset + + tal que +\begin_inset Formula $\forall x\in X,(\forall g,h\in G,x\cdot(gh)=(x\cdot g)\cdot h\land x\cdot1=x)$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $\cdot:G\times X\to X$ +\end_inset + + es una acción por la izquierda de +\begin_inset Formula $G$ +\end_inset + + en +\begin_inset Formula $X$ +\end_inset + + y +\begin_inset Formula $x\in X$ +\end_inset + +, llamamos +\series bold +órbita +\series default + de +\begin_inset Formula $x$ +\end_inset + + en +\begin_inset Formula $G$ +\end_inset + + a +\begin_inset Formula $G\cdot x\coloneqq\{g\cdot x\}_{g\in G}$ +\end_inset + + y +\series bold +estabilizador +\series default + de +\begin_inset Formula $x$ +\end_inset + + en +\begin_inset Formula $G$ +\end_inset + + a +\begin_inset Formula $\text{Estab}_{G}(x)\coloneqq\{g\in G\mid g\cdot x=x\}$ +\end_inset + +. + Si +\begin_inset Formula $\cdot:X\times G\to X$ +\end_inset + + es una acción por la derecha de +\begin_inset Formula $G$ +\end_inset + + en +\begin_inset Formula $X$ +\end_inset + + y +\begin_inset Formula $x\in X$ +\end_inset + +, llamamos órbita de +\begin_inset Formula $x$ +\end_inset + + en +\begin_inset Formula $G$ +\end_inset + + a +\begin_inset Formula $x\cdot G\coloneqq\{x\cdot g\}_{g\in G}$ +\end_inset + + y estabilizador de +\begin_inset Formula $x$ +\end_inset + + en +\begin_inset Formula $G$ +\end_inset + + a +\begin_inset Formula $\text{Estab}_{G}(x)\coloneqq\{g\in G\mid x\cdot g=x\}$ +\end_inset + +. + Las órbitas forman una partición de +\begin_inset Formula $G$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Llamamos +\series bold +acción por traslación a la izquierda +\series default + a la acción por la izquierda de +\begin_inset Formula $G$ +\end_inset + + en +\begin_inset Formula $G/H$ +\end_inset + + dada por +\begin_inset Formula $g\cdot xH=gxH$ +\end_inset + +. + Entonces +\begin_inset Formula $G\cdot xH=G/H$ +\end_inset + + y +\begin_inset Formula +\[ +\text{Estab}_{G}(xH)=[...]=H^{x^{-1}}. +\] + +\end_inset + +Análogamente llamamos +\series bold +acción por traslación a la derecha +\series default + a la acción por la derecha de +\begin_inset Formula $G$ +\end_inset + + en +\begin_inset Formula $H\backslash G$ +\end_inset + + dada por +\begin_inset Formula $Hx\cdot g=Hxg$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Cuando +\begin_inset Formula $H=1$ +\end_inset + +, la acción de traslación es de +\begin_inset Formula $G$ +\end_inset + + en +\begin_inset Formula $G$ +\end_inset + +, con +\begin_inset Formula $G\cdot x=G$ +\end_inset + + y +\begin_inset Formula $\text{Estab}_{G}(x)=1$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +La +\series bold +acción por conjugación +\series default + de +\begin_inset Formula $G$ +\end_inset + + en +\begin_inset Formula $G$ +\end_inset + + es la acción por la derecha +\begin_inset Formula $x\cdot g\coloneqq x^{g}$ +\end_inset + +. + Entonces +\begin_inset Formula $x\cdot G=x^{G}$ +\end_inset + + y +\begin_inset Formula $\text{Estab}_{G}(x)=C_{G}(x)$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $S$ +\end_inset + + es el conjunto de subgrupos de +\begin_inset Formula $G$ +\end_inset + +, la +\series bold +acción por conjugación de +\begin_inset Formula $G$ +\end_inset + + en sus subgrupos +\series default + es la acción por la derecha de +\begin_inset Formula $G$ +\end_inset + + en +\begin_inset Formula $S$ +\end_inset + + +\begin_inset Formula $H\cdot g=H^{g}$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $n\in\mathbb{N}$ +\end_inset + + y +\begin_inset Formula $X$ +\end_inset + + es un conjunto, +\begin_inset Formula $\cdot:S_{n}\times X^{n}\to X^{n}$ +\end_inset + + dada por +\begin_inset Formula $\sigma\cdot(x_{1},\dots,x_{n})\coloneqq(x_{\sigma(1)},\dots,x_{\sigma(n)})$ +\end_inset + + es una acción por la izquierda. +\end_layout + +\begin_layout Enumerate +Sean +\begin_inset Formula $\cdot:G\times X\to X$ +\end_inset + + una acción por la izquierda, +\begin_inset Formula $H\leq G$ +\end_inset + + e +\begin_inset Formula $Y\subseteq X$ +\end_inset + +, si +\begin_inset Formula $\forall h\in H,y\in Y,h\cdot y\in Y$ +\end_inset + +, +\begin_inset Formula $\cdot|_{H\times Y}$ +\end_inset + + es una acción por la izquierda de +\begin_inset Formula $H$ +\end_inset + + en +\begin_inset Formula $Y$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Sean +\begin_inset Formula $G$ +\end_inset + + un grupo actuando sobre un conjunto +\begin_inset Formula $X$ +\end_inset + +, +\begin_inset Formula $x\in X$ +\end_inset + + y +\begin_inset Formula $g\in G$ +\end_inset + +: +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\text{Estab}_{G}(x)\leq G$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $[G:\text{Estab}_{G}(x)]=|G\cdot x|$ +\end_inset + +. + En particular, si +\begin_inset Formula $G$ +\end_inset + + es finito, +\begin_inset Formula $|G\cdot x|\mid|G|$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Si la acción es por la izquierda, +\begin_inset Formula $\text{Estab}_{G}(g\cdot x)=\text{Estab}_{G}(x)^{g^{-1}}$ +\end_inset + +, y si es por la derecha, +\begin_inset Formula $\text{Estab}_{G}(x\cdot g)=\text{Estab}_{G}(x)^{g}$ +\end_inset + +. + En particular, si +\begin_inset Formula $x,g\in G$ +\end_inset + + y +\begin_inset Formula $H\leq G$ +\end_inset + +, +\begin_inset Formula $C_{G}(x^{g})=C_{G}(x)^{g}$ +\end_inset + + y +\begin_inset Formula $N_{G}(H^{g})=N_{G}(H)^{g}$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $R$ +\end_inset + + es un conjunto irredundante de representantes de las órbitas, +\begin_inset Formula $|X|=\sum_{r\in R}|G\cdot r|=\sum_{r\in R}[G:\text{Estab}_{G}(r)]$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Así, si +\begin_inset Formula $G$ +\end_inset + + es un grupo y +\begin_inset Formula $a\in G$ +\end_inset + +, +\begin_inset Formula $|a^{G}|=[G:C_{G}(a)]$ +\end_inset + +, y en particular +\begin_inset Formula $a^{G}$ +\end_inset + + es unipuntual si y sólo si +\begin_inset Formula $a\in Z(G)$ +\end_inset + +. + +\series bold +Ecuación de clases: +\series default + Si +\begin_inset Formula $G$ +\end_inset + + es finito y +\begin_inset Formula $X\subseteq G$ +\end_inset + + contiene exactamente un elemento de cada clase de conjugación con al menos + dos elementos, entonces +\begin_inset Formula $|G|=|Z(G)|+\sum_{x\in X}[G:C_{G}(x)]$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Dado un número primo +\begin_inset Formula $p$ +\end_inset + +, un +\series bold + +\begin_inset Formula $p$ +\end_inset + +-grupo +\series default + es un grupo en que todo elemento tiene orden potencia de +\begin_inset Formula $p$ +\end_inset + +, y un grupo finito es un +\begin_inset Formula $p$ +\end_inset + +-grupo si y sólo si su orden es potencia de +\begin_inset Formula $p$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Standard + +\series bold +Teorema de Cauchy: +\series default + Si +\begin_inset Formula $G$ +\end_inset + + es un grupo finito con orden múltiplo de un primo +\begin_inset Formula $p$ +\end_inset + +, +\begin_inset Formula $G$ +\end_inset + + tiene un elemento de orden +\begin_inset Formula $p$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Standard +Dados un grupo finito +\begin_inset Formula $G$ +\end_inset + + y un número primo +\begin_inset Formula $p$ +\end_inset + +, +\begin_inset Formula $H\leq G$ +\end_inset + + es un +\series bold + +\begin_inset Formula $p$ +\end_inset + +-subgrupo de Sylow +\series default + de +\begin_inset Formula $G$ +\end_inset + + si es un +\begin_inset Formula $p$ +\end_inset + +-grupo y +\begin_inset Formula $[G:H]$ +\end_inset + + es coprimo con +\begin_inset Formula $p$ +\end_inset + +, si y sólo si es un +\begin_inset Formula $p$ +\end_inset + +-grupo y +\begin_inset Formula $|H|$ +\end_inset + + es la mayor potencia de +\begin_inset Formula $p$ +\end_inset + + que divide a +\begin_inset Formula $|G|$ +\end_inset + +. + Llamamos +\begin_inset Formula $s_{p}(G)$ +\end_inset + + al número de +\begin_inset Formula $p$ +\end_inset + +-subgrupos de Sylow de +\begin_inset Formula $G$ +\end_inset + +. +\end_layout + +\begin_layout Standard + +\series bold +Teoremas de Sylow: +\series default + Sean +\begin_inset Formula $p$ +\end_inset + + un número primo y +\begin_inset Formula $G$ +\end_inset + + un grupo finito de orden +\begin_inset Formula $n\coloneqq p^{k}m$ +\end_inset + + para ciertos +\begin_inset Formula $k,m\in\mathbb{N}$ +\end_inset + + con +\begin_inset Formula $p\nmid m$ +\end_inset + +. + Entonces: +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $G$ +\end_inset + + tiene al menos un +\begin_inset Formula $p$ +\end_inset + +-subgrupo de Sylow, que tendrá orden +\begin_inset Formula $p^{k}$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $P$ +\end_inset + + es un +\begin_inset Formula $p$ +\end_inset + +-subgrupo de Sylow de +\begin_inset Formula $G$ +\end_inset + + y +\begin_inset Formula $Q$ +\end_inset + + es un +\begin_inset Formula $p$ +\end_inset + +-subgrupo de +\begin_inset Formula $G$ +\end_inset + +, existe +\begin_inset Formula $g\in G$ +\end_inset + + tal que +\begin_inset Formula $Q\subseteq P^{g}$ +\end_inset + +. + En particular, todos los +\begin_inset Formula $p$ +\end_inset + +-subgrupos de Sylow de +\begin_inset Formula $G$ +\end_inset + + son conjugados en +\begin_inset Formula $G$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $s_{p}(G)\mid m$ +\end_inset + + y +\begin_inset Formula $s_{p}(G)\equiv1\bmod p$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +end{reminder} +\end_layout + +\end_inset + + +\end_layout + +\end_body +\end_document |
