В.А. Артамонов - Лекции по алгебре, 3 семестр, мех-мат МГУ (1106002), страница 2
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âáî¤ ¢ë⥪ ¥â (2), ¨, á«¥¤®¢ ⥫ì®, (1).â ª, ¯¥à¢ë¥ âਠãá«®¢¨ï íª¢¨¢ «¥âë. «®£¨ç® ¯®ª §ë¢ ¥âáï, çâ® ç¥â¢¥à⮥ãá«®¢¨¥ íª¢¨¢ «¥â® ¢â®à®¬ã.¯à¥¤¥«¥¨¥ 1.44. ãáâ쬮¦¥á⢮ ¢á¥å â ª¨åx ∈ G,।«®¦¥¨¥ 1.45.f :G→H {f (x) = 1.£®¬®¬®à䨧¬ £à㯯.¤à®¬ker f §ë¢ ¥âáïçâ®ker f / G.ਬ¥àë 1.46. ®ª § âì, çâ®(1)(2)(3)An / Sn ;SL(n, C) / GL(n, C);V 4 / S 4 , S3 6 S4 .f :G→H⇐⇒ ker f = 1.¯à ¦¥¨¥ 1.47. ãáâìf¦¥¨¥¨ê¥ªâ¨¢®à¥¤«®¦¥¨¥ 1.48.ãáâì{ £®¬®¬®à䨧¬ £à㯯.®ª § âì, çâ® ®â®¡à -f : G → H { £®¬®¬®à䨧¬ £à㯯 ¨ x ∈ G. ®£¤ f −1 (f (x)) = x ker f .®ª § ⥫ìá⢮.
¬¥â¨¬, çâ® ¢ ᨫã ã¯à ¦¥¨ï 1.29y ∈ f −1 (f (x)) ⇐⇒ f (y) = f (x) ⇐⇒ f (x−1 y) = 1⇐⇒ x−1 y ∈ ker f ⇐⇒ x ker f = y ker f.âáî¤ ¢ë⥪ ¥â ã⢥ত¥¨¥®áâ஥¨¥ä ªâ®à£à㯯ëG/N , £¤¥ N / G.®áâ஥¨¥¥áâ¥á⢥®£® £®¬®¬®à䨧¬ π : G → G/N .¯à ¦¥¨¥ 1.49. ᫨π : G → G/N{ ¥áâ¥áâ¢¥ë© £®¬®¬®à䨧¬, ⮥®à¥¬ 1.50 (¥®à¥¬ ® £®¬®¬®à䨧¬ å).®£¤ ãáâìker π = N .f : G → H { £®¬®¬®à䨧¬ £à㯯.G/ ker f ' f (G).x ∈ G. ® ¯à¥¤«®¦¥¨î 1.48 ¯®«ãç ¥¬,®â®¡à ¦¥¨¥ ζ : f (G) → G/ ker f ¯® ¯à ¢¨«ã®ª § ⥫ìá⢮. ãáâìx ker f . ¤ ¤¨¬ ⥯¥àìçâ®f −1 (f (x)) =ζ(f (x)) = f −1 (f (x)) = x ker f.஢¥à¨¬, çâ®ζï¥âáï £®¬®¬®à䨧¬®¬ £à㯯.
ãáâìx, y ∈ G.®£¤ â. ¥.ζ(f (xy)) = xy(ker f ) = (x ker f )(y ker f ) = ζ(f (x))ζ(f (y)).â ª,ζï¥âáï £®¬®¬®à䨧¬®¬.xy ∈ f −1 (f (xy)),101. ζ¡¥¤¨¬áï, çâ®g = f (x), h = f (y)f (y) = h.¡¥¤¨¬áï, ç⮨ꥪ⨢®.¤«ï ¥ª®â®àëåζãáâìx, y ∈ G.áîàꥪ⨢®. ᫨g, h ∈ f (G) ¨ ζ(g) = ζ(h). ® ®¯à¥¤¥«¥¨îâáî¤ x ker f = y ker f , ¨ ¯®í⮬ã g = f (x) =x ∈ G, â® x ker f = ζ(f (x)).
â ª, ζ{ ¨§®¬®à䨧¬.ਬ¥àë 1.51. ®ª § âì, çâ®(1)(2)(3)GL(n, C)/ SL(n, C) ' C∗ ;Sn /An ' {±1};Z/nZ ' Un .4. ¥©áâ¢¨ï £à㯯 ¬®¦¥á⢠å¯à¥¤¥«¥¨¥ 1.52. ãáâì X,GG × X → X,çâ®{ £à㯯 ¨X{ ¬®¦¥á⢮. ª ¦¥¬, çâ®G ¤¥©áâ¢ã¥â¥á«¨ § ¤ ® â ª®¥ ®â®¡à ¦¥¨¥(g, x) 7→ gx ∈ X,g ∈ G, x ∈ X,1x = x, (gh)x = g(h(x)) ¤«ï ¢á¥å g, h ∈ G ¨ x ∈ X.G ¢ £à㯯㠯¥à¥áâ ®¢®ª ¬®¦¥á⢠X .à㣨¬¨ á«®¢ ¬¨, § ¤ £®¬®¬®à-䨧¬ £à㯯ëਬ¥àë 1.53.G ᮯà殮¨ï¬¨ G.H { ¯®¤£à㯯 ¢ G.
®£¤ H ¤¥©áâ¢ã¥â 㬮¦¥¨ï¬¨ á«¥¢ X = G.à㯯 G = GL(n, C) ¤¥©áâ¢ã¥â n-¬¥à®¬ ¢¥ªâ®à®¬ ª®¬¯«¥ªá®¬ ¯à®áâà áân¢¥ C .] à㯯 Sn ¤¥©áâ¢ã¥â ª®«ìæ¥ ¬®£®ç«¥®¢ C[X1 , . . . , Xn ] ¯® ¯à ¢¨«ãz[\¥©á⢨¥ £à㯯ëãáâìσ(f (X1 , . . . , Xn )) = f (Xσ1 , . . . , Xσn ).G ¬®¦¥á⢥ X , ¨ x ∈ X .{gx|g ∈ G}. â ¡¨«¨§ â®à®¬ Stxgx = x.¯à¥¤¥«¥¨¥ 1.54. ãáâì § ¤ ® ¤¥©á⢨¥ £à㯯ëࡨ⮩Orbxí«¥¬¥â x §ë¢ ¥âáï ¯®¤¬®¦¥á⢮ §ë¢ ¥âáï ¯®¤¬®¦¥á⢮ ¢á¥å â ª¨åg ∈ G,çâ®à¥¤«®¦¥¨¥ 1.55.
á«ãç ¥ ¤¥©á⢨ï z ®à¡¨â Orbx ᮢ¯ ¤ ¥â á ª« áᮬ ᮯà殮ëå í«¥¬¥â®¬ {gxg −1 |g ∈ G}. â ¡¨«¨§ â®à Stx í«¥¬¥â x ∈ G ᮢ¯ ¤ ¥â áæ¥âà «¨§ â®à®¬ C(x) = {g ∈ G|gx = xg}. á«ãç ¥ ¤¥©á⢨ï [ ®à¡¨â Orbx ᮢ¯ ¤ ¥â á ¯à ¢ë¬ á¬¥¦ë¬ ª« áᮬ Hx. â ¡¨«¨§ â®à Stx í«¥¬¥â x ∈ G à ¢¥ 1.।«®¦¥¨¥ 1.56. §ë¥ ®à¡¨âë ¥ ¯¥à¥á¥ª îâáï.।«®¦¥¨¥ 1.57. ãáâì § ¤ ® ¤¥©á⢨¥ £à㯯ë G ¬®¦¥á⢥ãé¥áâ¢ã¥â ¡¨¥ªæ¨ï ¬¥¦¤ã Orbx ¨ ¬®¦¥á⢮¬ «¥¢ëå ᬥ¦ëå ª« áᮢ®ª § ⥫ìá⢮.
ãáâì«¥¤á⢨¥ 1.58.g ∈ G.| Orbx | =®¯®áâ ¢¨¬ í«¥¬¥âãgx ∈ OrbxgStx .|G|.| Stx |G ¬®¦¥á⢥ X ,x ¥¯®¤¢¨¦ ®â®á¨â¥«ì® í⮣® ¤¥©á⢨ï, ¥á«¨ Stx = G, â.¯à¥¤¥«¥¨¥ 1.59. ãáâì § ¤ ® ¤¥©á⢨¥ £àã¯¯ëª ¦¥¬, çâ® â®çª ª« ááX, ¨ x ∈ X.G ¯® Stx .¨¥.x ∈ X.Orbx =x. ¬¥ç ¨¥ 1.60. á«ãç ¥ ¤¥©á⢨ïà¨ç¥áª¨¥ ¬®£®ç«¥ë ¨ ⮫쪮 ®¨.ïîâáï í«¥¬¥âë æ¥âà ¬¥ç ¨¥ 1.61.]¥¯®¤¢¨¦ë¬¨ í«¥¬¥â ¬¨ ïîâáï ᨬ¬¥â-z∀g ∈ G} á«ãç ¥ ¤¥©á⢨ïZ(G) = {x ∈ G|gx = xg¥¯®¤¢¨¦ë¬¨ í«¥¬¥â ¬¨4.
Å11¯à ¦¥¨¥ 1.62. ©â¨ æ¥âàë £à㯯GL(n, k), SL(n, k), O(n, R), U(n, C). ¦¤ ï ¯¥à¥áâ ®¢ª ¨§¥®à¥¬ 1.63.Sn à §« £ ¥âáï ¢ ¯à®¨§¢¥¤¥¨¥ ¥§ ¢¨á¨¬ë忍ª«®¢.ãáâì σ ∈ Sn . ®¦® áç¨â âì, çâ® σ 6= 1. ®§ì¬¥¬ ¯à®¨§¢®«ìë© í«¥¬¥â k, 1 ≤k ≤ n, ¨ ¯à¥¤¯®«®¦¨¬, çâ® í«¥¬¥âë k0 = k, k1 = σk, k2 = σ 2 k, . . . , kl = σ l k à §«¨çë, ®σ l+1 k = σ s k , £¤¥ 0 ≤ s ≤ l.¥¬¬ 1.64.s = 0.®ª § ⥫ìá⢮.¬®¦®, ¨¡®σâ ª, ¬®¦¥á⢥s > 0, â® σ(ks−1 ) = σ(kl ), çâ® ¥¢®§X = {1, . .
. , n}, ® ks−1 6= kl ¢ ᨫ㠢롮à l.®ª § ⥫ìá⢮. ᫨¤¥©áâ¢ã¥â ¨ê¥ªâ¨¢® {k0 , k1 , . . . , kl } ¯®¤áâ ®¢ª σ ¤¥©áâ¢ã¥âk0 k1 . . . kl−1 klk1 k2 . . .klk0ª ªj, 1 ≤ j ≤ n, ¯à¨ç¥¬ j ∈/ {k0 , k1 , . . . , kl }. ª{j0 , j1 , . . . , jt }, ª®â®à®¬ ¯®¤áâ ®¢ª σ ¤¥©áâ¢ã¥â ª ª 横«j0 j1 . .
. jt−1 jtj1 j2 . . .jtj0롥६ ⥯¥àì ¯à®¨§¢®«ì®¥ ç¨á«®áâந¬ ¬®¦¥á⢮¥¬¬ 1.65.á¥ í«¥¬¥â뮪 § ⥫ìá⢮. ãáâì¨ ¢ëè¥k0 , k1 , . . . , kl , j0 , j1 , . . . , jt à §«¨çë.jr = kq .j0 = σ−r®£¤ jr ∈ {k0 , k1 , . . . , kl },çâ® ¥¢®§¬®¦®.த®«¦ ï íâ®â ¯à®æ¥áá, ¯®«ãç ¥¬ ¯®¤áâ ®¢ªãτ=k0k1k1k2. . . kl−1...klklk0j0j1¥¯®á।á⢥ ï ¯à®¢¥àª ¯®ª §ë¢ ¥â, çâ®j1j2. .
. jt−1...jtjt··· .j0τ = σ.¯à ¦¥¨¥ 1.66. ®ª § âì, çâ®σ = σ1 · · · σm { à §«®¦¥¨¥ ¯¥à¥áâ ®¢ª¨ σ ∈ Sn ¢ ¯à®¨§¢¥¤¥¨¥ ¥§ ¢¨á¨¬ëå|σ| à ¢¥ ¨¡®«ì襬㠮¡é¥¬ã ¤¥«¨â¥«î ¤«¨ σ1 , . . . , σm ;¥§ ¢¨á¨¬ëå æ¨ª« ¨§ Sn ¯¥à¥áâ ®¢®çë.(1) ¥á«¨æ¨ª«®¢, â®(2) ¤¢ ।«®¦¥¨¥ 1.67.ãáâìπ ∈ Sn ¨ (i1 , . . . , ik ) { 横« ¨§ Sn . ®£¤ π(i1 , . . . , ik )π −1 = (π(i1 ), . .
. , π(ik )).¥®à¥¬ 1.68. ¢¥ ¯¥à¥áâ ®¢ª¨ ¨§¨¬¥îâ ®¤¨ ª®¢®¥ 横«®¢®¥ áâ஥¨¥.Sn ᮯà殮ë ⮣¤ ¨ ⮫쪮 ⮣¤ , ª®£¤ ®¨®ª § ⥫ìá⢮. «ï ¤®ª § ⥫ìá⢠¥®¡å®¤¨¬®á⨠㦮 ¢®á¯®«ì§®¢ âìáï ¯à¥¤«®¦¥¨¥¬ 1.67. ¡à â®, ¯ãáâì ¯®¤áâ ®¢ª¨σ, τ¨¬¥îâ ®¤¨ ª®¢®¥ 横«®¢®¥ áâ஥¨¥, â.¥.σ = (k0 , k1 , . . . , kl )(j0 , j1 , . . . , jt ) · · · ,τ = (k00 , k10 , . .
. , kl0 )(j00 , j10 , . . . , jt0 ) · · · .® ¯à¥¤«®¦¥¨î 1.67 ¨¬¥¥¬π=πσπ −1 = τ ,k0k00k1k10£¤¥. . . kl. . . kl0j0j00j1j10. . . jt. . . jt0.......121. ᫨¥®à¥¬ 1.69.n ≥ 3, â® Z(Sn ) = 1.®ª § ⥫ìá⢮. ãáâìσ ∈ Z(Sn ) \ 1,¨σ = (i1 , . . . , ik )(j1 , . . .
, jt ) · · ·{ à §«®¦¥¨¥σ¢ ¯à®¨§¢¥¤¥¨¥ ¥§ ¢¨á¨¬ëå æ¨ª«®¢. ãáâì ¢ í⮬ à §«®¦¥¨¨ ¢áâà¥ç -îâáï ¤¢ 横« ¤«¨k, t ≥ 2.®«®¦¨¬π = (i1 , j1 ). ®£¤ π −1 = π , ¨ ¯® ¯à¥¤«®¦¥¨î 1.67πσπ −1 = (j1 , i2 , . . . , ik )(i1 , j2 , . . . , jt ) · · · 6= σ,çâ® ¯à®â¨¢®à¥ç¨â ãá«®¢¨îσ ∈ Z(Sn ).â ª,ï¥âáï æ¨ª«®¬. ᫨ ¥£® ¤«¨ σ = (i1 , . . . , ik )k ≥ 3, â® ¯®«®¦¨¬ π = (i1 , i2 ).®£¤ π −1 = π ,¨ ¯®¯à¥¤«®¦¥¨î 1.67πσπ −1 = (i2 , i1 , i3 , . .
. , ik ) 6= σ,çâ® ¯à®â¨¢®à¥ç¨â ãá«®¢¨î σ ∈ Z(Sn ).â ª, σ = (i1 , i2 ). ª ª ª n ≥ 3, â® ©¤¥âáï ¨¤¥ªá i3 ,π = (i1 , i3 ). ®£¤ ¯® ¯à¥¤«®¦¥¨î 1.67®â«¨çë© ®âi1 , i3 .®«®¦¨¬πσπ −1 = (i3 , i2 ) 6= σ,çâ® ¯à®â¨¢®à¥ç¨â ãá«®¢¨îσ ∈ Z(Sn ).¯à ¦¥¨¥ 1.70.
®ª § âì, çâ® ¤¢¥ ¬ âà¨æë ¨§GL(n, C)ᮯà殮ë (¯®¤®¡ë)⮣¤ ¨ ⮫쪮 ⮣¤ , ª®£¤ ®¨ ¨¬¥îâ ®¤¨ ª®¢ë¥ ¦®à¤ ®¢ë ä®à¬ë.¯à¥¤¥«¥¨¥ 1.71. ãáâìp{ ¯à®á⮥ ç¨á«®.à㯯 ¯®à浪 pn §ë¢ ¥âáïp-£à㯯®©.¥®à¥¬ 1.72.¥âàp-£à㯯ë G ¥âਢ¨ «¥.®ª § ⥫ìá⢮. ãáâìG = K1 ∪ . . . ∪ Km { à §«®¦¥¨¥ G ¥¯¥à¥á¥ª î騥áï|Ki | = 1 ⮣¤ ¨ ⮫쪮 ⮣¤ , ª®£¤ Ki =ª« ááë ᮯà殮ëå í«¥¬¥â®¢. ¬¥â¨¬, çâ®{ai },£¤¥ai ∈ Z(G).âáî¤ G = Z(G) ∪ Kr ∪ . .
. ∪ Km ,® á«¥¤á⢨î 1.58 ¯®à冷ªâáî¤ ¯® (1) ç¨á«®p|Ki ||Ki | > 1.¤¥«¨â ¯®à冷ª £à㯯뤥«¨â ¯®à冷ªG,â.Z(G).(1)¥.ni|Ki | = p , n > ni > 0.5. ¥®à¥¬ë ¨«®¢ ãáâì G { ª®¥ç ï £à㯯 ¯®à浪 áãé¥áâ¢ã¥â ¯®¤£à㯯 ¯®à浪 pn .¥®à¥¬ 1.73 (¥à¢ ï ⥮६ ¨«®¢ ).£¤¥p { ¯à®á⮥ ç¨á«®. ®£¤ ¢ Gpn m,®ª § ⥫ìá⢮. 㤥¬ ¢¥á⨠¤®ª § ⥫ìá⢮ ¨¤ãªæ¨¥© ¯® ¯®à浪㠣à㯯ë«ãç ©|G| = pnx ∈ G \ Z(G).
áᬮâਬ ¤¥©á⢨¥ G1 < | Orbx | < |G| ¨ |G| = | Orbx || Stx |. ®í⮬㠥᫨ p ¥ ¤¥«¨â| Stx |, ¯à¨ç¥¬ | Stx | < |G|. ® ¨¤ãªæ¨¨ ¢ Stx áãé¥áâ¢ã¥â ¯®¤£à㯯 ।¯®«®¦¨¬ á ç « , çâ® áãé¥áâ¢ã¥â í«¥¬¥âᮯà殮¨ï¬¨ | Orbx |,¯®à浪 pnâ®pãáâìnG.¤¥«¨â®£¤ , ¨ ⥮६ ¤®ª § .p¤¥«¨â| Orbx |x ∈ G \ Z(G).
®£¤ ª ªX|G| = |Z(G)| +| Orbx |.¤«ï «î¡®£®x∈G\Z(G) ª¨¬ ®¡à §®¬,G.®ç¥¢¨¤¥.p¤¥«¨â ¯®à冷ªZ(G).¨ ¢ (1) ¨¬¥¥¬5. ¥¬¬ 1.74.13Z(G) áãé¥áâ¢ã¥â í«¥¬¥â ¯®à浪 p.®ª § ⥫ìá⢮. ®ª § ⥫ìá⢮ ¡ã¤¥¬ ¢¥á⨠¨¤ãªæ¨¥© ¯® ¯®à浪ã|Z(G)| = p, â® ã⢥ত¥¨¥ ®ç¥¢¨¤®. ãáâì |Z(G)| > p,çâ® p ¥ ¤¥«¨â ¯®à冷ª a. ®£¤ N = hai / Z(G), ¯à¨ç¥¬Z(G)/Ní«¥¬¥âbZ(G)/N¯®«ãç ¥¬, çâ®bN, b ∈ Z(G),¨¬¥¥âáï í«¥¬¥â¨¬¥¥â ¯®à冷ªd.®£¤ a ∈ Z(G) \ 1.|Z(G)|. ᫨।¯®«®¦¨¬,|Z(G)|< |Z(G)|.|N ||Z(G)/N | =® ¨¤ãªæ¨¨ ¢¨bd = 1.¯®à浪 p.¯à¥¤¯®«®¦¨¬, çâ®à¨ ¥áâ¥á⢥®¬ £®¬®¬®à䨧¬¥π : Z(G) →(bN )d = π(b)d = π(bd ) = π(1) = N.p = |bN | ¤¥«¨â d.í«¥¬¥â b ¯®à浪 d, ¤¥«ï饣®áï®í⮬㠢 ᨫ㠯।«®¦¥¨ï 1.14â ª, ¢Z(G)¢á¥£¤ ¥áâì ¢¥à訬 ¤®ª § ⥫ìá⢮ ⥮६ë.
ãáâìa ∈ Z(G) dp.®£¤ ⮨¬¥¥â ¯®à冷ªp,¨|b p | = p. N = hai / G.®£¤ |G||G|=.|N |pn−1® ¨¤ãªæ¨¨ ¢ G/N ¨¬¥¥âáï ¯®¤£à㯯 U ¯®à浪 p. ãáâì H = {y ∈ G|yN ∈ U }. áᬮâਬ ¥áâ¥áâ¢¥ë© £®¬®¬®à䨧¬ π : H → U, π(z) = zN. ® ⥮६¥ ® £®¬®¬®à䨧¬ åU ' H/N , ¨ ¯®í⮬ã |H| = |U ||N | = pn .|G/N | =¯à¥¤¥«¥¨¥ 1.75. ãáâì(p, m) = 1.¯à¨ç¥¬G{ ª®¥ç ï £à㯯 ¯®à浪 ®¤£à㯯 ¯®à浪 pn¢G §ë¢ ¥âáïpn m,p { ¯à®á⮥ ç¨á«®,p-¯®¤£à㯯®©.£¤¥á¨«®¢áª®©¥®à¥¬ 1.76 (â®à ï ⥮६ ¨«®¢ ). ãáâì G { ª®¥ç ï £à㯯 , ¨ p { ¯à®á⮥ç¨á«®. ®£¤ «î¡ ï p-¯®¤£à㯯 ¢ G ᮤ¥à¦¨âáï ¢ ¥ª®â®à®© ᨫ®¢áª®© p-¯®¤£à㯯¥.î¡ë¥ ¤¢¥ ᨫ®¢áª¨¥ p-¯®¤£à㯯ë ᮯàï¦¥ë ¢ G.®ª § ⥫ìá⢮. ãáâì Γ ¯à®¨§¢®«ì ï p-¯®¤£à㯯 ¢ G ¨ P { ᨫ®¢áª ïp-¯®¤£à㯯 ¢ G.