А.В. Михалёв - Лекции по высшей алгебре (1106006), страница 3
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¥.(H, g) → g −1 Hg, g ∈ G£à㯯 G ¤¥©áâ¢ã¥â ¬®¥á⢥ ¢á¥å ¯®¤£à㯯 H £à㯯ë G ᮯà泌¥¬). ᨫ㠢â®à®© â¥®à¥¬ë ¨«®¢ ¢á¥ ᨫ®¢áª¨¥ p-¯®¤£àã¯¯ë ®¡à §ãîâ ®¤ã ¨§ ®à¡¨â Orb(S) ¢ MG,£¤¥ S — ®¤ ¨§ ᨫ®¢áª¨å ¯®¤£à㯯 £à㯯ë G, n(p) = | Orb(S)|. ª ª ª |G| = | St(S)| · | Orb(S)|,â® ïá®, çâ® n(p) = | Orb(S)| — ¤¥«¨â¥«ì ç¨á« n = |G|.2) áᬮâਬ ⥯¥àì ¬®¥á⢮ ¢á¥å ᨫ®¢áª¨å p-¯®¤£à㯯 ΣS = {S1 , . . . , Sn (p)}S ª ª ¯à ¢ë©S1 -¯®«¨£® (§¤¥áì S = S1 ) á ᮯà泌¥¬:1(Si , a) → a−1 Si a,Si ∈ Σ, a ∈ S11(ïá®, çâ® |a−1 Si a| = |Si | = pk , â. ¥.
a−1 Si a ∈ Σ). ) á®, çâ® a−1 S1 a = S1 ¤«ï a ∈ S1 , â. ¥. S1 — ¥¤¨á⢥ ï ¥¯®¤¢¨ ï â®çª ¢ Σ ¯à¨¤¥©á⢨¨ £à㯯ë S1 (â. ¥. ¥¤¨á⢥ ï ®¤®í«¥¬¥â ï ®à¡¨â ¢ ΣS1 ).¥©á⢨⥫ì®, ¤®¯ãá⨬ ¯à®â¨¢®¥, â. ¥. çâ® | Orb(Si)| = 1 ¤«ï i 6= 1, â. ¥. a−1 Sia = Si ¤«ï¢á¥å a ∈ S1 . «¥¤®¢ ⥫ì®, S1 Si = Si S1 , ¨ ¯®í⮬㠯®¤¬®¥á⢮ H = SiS1 = S1 Si ï¥âáﯮ¤£à㯯®© (¢ ᨫ㠤®ª § ®£® à ¥¥ ªà¨â¥à¨ï ® ⮬, ª®£¤ ¯à®¨§¢¥¤¥¨¥ ¯®¤£à㯯 ï¥âáﯮ¤£à㯯®©).DZ® ⥮६¥ £à ¤«ï ¯®¤£à㯯 H ¨¬¥¥¬: |G| = |H| · [G : H], â ª¨¬ ®¡à §®¬, S1 ¨ Siâ ª¥ ïîâáï ᨫ®¢áª¨¬¨ p-¯®¤£à㯯 ¬¨ ¨ ¢ £à㯯¥ H; ¯à¨¬¥ïï ª ¨¬ ¢ £à㯯¥ H 2-î ⥮६㨫®¢ , ¯®«ãç ¥¬, çâ® S1 = h−1 Sih ¤«ï h ∈ H h = ab ∈ H = S1 Si, a ∈ S1 , b ∈ Si.® ⮣¤ S1 = h−1 Si h = (ab)−1 Si (ab) = b−1 (a−1 Si a)b = b−1 Si b = Si (§¤¥áì ¬ë ¨á¯®«ì§®¢ «¨à ¢¥á⢮ a−1 Si a = Si , ¯®áª®«ìªã Si — ®à¡¨â , á®áâ®ïé ï ¨§ ®¤®£® í«¥¬¥â ) çâ® ¯à®â¨¢®à¥ç¨â⮬ã, çâ® i > 1, â.
¥. Si 6= S1 .¡) ¢¥à襨¥ ¤®ª § ⥫ìá⢠3-© â¥®à¥¬ë ¨«®¢ .â ª, à áᬠâਢ ï ¤«ï ¯®«¨£® ΣS1 = {S1, . . . , Sn(p) } à §¡¨¥¨¥ ®à¡¨âë, ¨¬¥¥¬ ¥¤¨á⢥ãî ®¤®í«¥¬¥â àãî ®à¡¨âã Orb(S1 ) = {S1}, ¯à¨ í⮬ ¯à¨ i > 1 ¤«ï ¤àã£¨å ®à¡¨â (ᮤ¥à é¨å¡®«¥¥ ®¤®£® í«¥¬¥â )pk = |S1 | = | St(Si )|| Orb(Si )|,8¥ªæ¨ï 9http://mmresource.nm.ru/â. ¥. ç¨á«® í«¥¬¥â®¢ íâ¨å ®à¡¨â å ¤¥«¨âáï p (ª ª ¤¥«¨â¥«ì ç¨á« pk ). ª¨¬ ®¡à §®¬,n(p) = 1 + pq.«¥¤áâ¢¨ï ¨§ â¥®à¥¬ë ¨«®¢ «¥¤á⢨¥ 1. ª®¥ç®© £à㯯¥ ᨫ®¢áª ï p-£à㯯 ¥¤¨á⢥ (â. ¥. n(p) = 1) ⮣¤ ¨â®«ìª® ⮣¤ , ª®£¤ íâ ᨫ®¢áª ï ¯®¤£à㯯 ï¥âáï ®à¬ «ì®© ¯®¤£à㯯®©.«¥¤á⢨¥ 2 (®¡à 饨¥â¥®à¥¬ë £à ¤«ïª®¥çëå p-k £à㯯).
DZãáâì G — ª®kl¥ç ï p-£à㯯 , |G| = p . ®£¤ ¤«ï «î¡®£® ¤¥«¨â¥«ï p , l ≤ k, ç¨á« p áãé¥áâ¢ã¥â ¯®¤£à㯯 H£à㯯ë G â ª ï, çâ® |H| = pl .®ª § ⥫ìá⢮ (¨¤ãªæ¨¥© ¯® k). «ãç © k = 0 ïá¥. DZãáâì |G| = pk > 1. ᨫã â¥®à¥¬ë® æ¥âॠZ(G) p-£à㯯ë G: |Z(G)| > 1. ᨫã á«¥¤áâ¢¨ï ¨§ áâàãªâãன â¥®à¥¬ë ¤«ï ª®¥ç®© ¡¥«¥¢®© £à㯯ë Z(G) ¨¬¥¥â ¬¥áâ® ®¡à 饨¥ â¥®à¥¬ë £à .
ç áâ®á⨠¤«ï ¤¥«¨â¥«ï pç¨á« pl = |H| ©¤ñâáï æ¨ª«¨ç¥áª ï ¯®¤£à㯯 (c) ¨§ p í«¥¬¥â®¢ ¢ £à㯯¥ Z(G). á®, çâ®(c) ⊳ G. ®£¤ ¤«ï ä ªâ®à£à㯯ë Ḡ = G/(c) ¨¬¥¥¬: |Ḡ| = |G|/p = pk−1 . ᨫ㠨¤ãªâ¨¢®£®¯à¥¤¯®«®¥¨ï (â ª ª ª pk−1 < pk ), ¢ Ḡ ©¤ñâáï ¯®¤£à㯯 H̄ â ª ï, çâ® |H̄| = pl−1 , ¯à¨ í⮬H̄ = H/(c), £¤¥ H — ¯®¤£à㯯 £à㯯ë G â ª ï, çâ® (c) ⊆ H ⊂ G. ª ª ªâ® ¯®¤£à㯯 H ï¥âáï ¨áª®¬®©.|H| = |H̄||(c)| = pl−1 · p = pl ,DZਬ¥à ¯à¨¬¥¥¨ï ⥮६ ¨«®¢ (横«¨ç®áâì £àã¯¯ë ¨§ 15 í«¥¬¥â®¢). DZãáâìG — ª®¥ç ï £à㯯 , |G| = 15 = 3 · 5.
áᬠâਢ ï ¢á¥ ¤¥«¨â¥«¨ 1, 3, 5, 15 ç¨á« 15 ¢¨¤¨¬çâ® n(3) = 1 ¨ n(5) = 1. DZ®í⮬ã áãé¥áâ¢ãîâ ¥¤¨áâ¢¥ë¥ (¨ ¯®í⮬㠮ଠ«ìë¥ á¨«®¢áª¨¥3-¯®¤£à㯯 A ¨ 5-¯®¤£à㯯 B.§ A ⊳ G, B ⊳ á«¥¤ã¥â, çâ® AB — ¯®¤£à㯯 . ª ª ª |A| = 3, |B| = 5, â® A ∼= Z3 , B ∼= Z5 ,|A ∩ B| = 1, â. ¥. A ∩ B = {e}. DZ®í⮬ã AB = A × B ¨ |AB| = 3 × 5 = 15, â. ¥. AB = G. â ª,G = A×B ∼= Z3 ⊕ Z5 ∼= Z15 , â. ¥. áãé¥áâ¢ã¥â «¨èì ¥¤¨á⢥ ï (á â®ç®áâìî ¤® ¨§®¬®à䨧¬ )ª®¥ç ï £à㯯 ¨§ 15 í«¥¬¥â®¢ — 横«¨ç¥áª ï £à㯯 Z15 . . 1) ®ª § âì, çâ® ¥á«¨ |G| = 175 = 52 · 7, â® £à㯯 G ¡¥«¥¢ .2) ¯¨á âì ¢á¥ £àã¯¯ë ¨§ 12 í«¥¬¥â®¢.3) ᫨ |G| < ∞ ¨ ¯®à冷ª |G| £à㯯ë G ¥ ï¥âáï ¯à®áâë¬ ç¨á«®¬, â® £à㯯 G ᮤ¥à¨â¥âਢ¨ «ìãî ®à¬ «ìãî ¯®¤£à㯯ã (â. ¥.
G ¥ ï¥âáï ¯à®á⮩ £à㯯®©). à㣨¬¨ á«®¢ ¬¨£à㯯 A5 , |A5 | = 60 ï¥âáï, ª ª ¬ë ¢áª®à¥ 㢨¤¨¬, ï¥âáï á ¬®© ¬ «¥ìª®© ¥ª®¬¬ãâ ⨢®©¯à®á⮩ £à㯯®©.. ᫨ p — ¯à®á⮥ ç¨á«®, â®¯à ¥¨¥¥®à¥¬ ¨«á® ®ª § ⥫ìá⢮. DZãáâì(p − 1)! ≡ −1(mod p).G = Sp — £à㯯 ¯®¤áâ ®¢®ª p í«¥¬¥â®¢, |G| = p! = p(p − 1)!,®£¤ ᨫ®¢áª ï p-¯®¤£à㯯 ¢ Sp ᮤ¥à¨â p í«¥¬¥â®¢, ¨ ¯®í⮬ã ï¥âáïæ¨ª«¨ç¥áª®© £à㯯®© ¯®à浪 p. «¥¬¥âë ¯®à浪 p ¢ £à㯯¥ Sp — íâ®, ¢ â®ç®áâ¨, 横«ë¤«¨ë p, ¨å ç¨á«® à ¢® p!/p = (p − 1)!. ª ¤®© 横«¨ç¥áª®© £à㯯¥ ¯®à浪 p, ¯à¨ í⮬ à §«¨çë¥ æ¨ª«¨ç¥áª¨¥ ¯®¤£àã¯¯ë ¯®à浪 p ¨¬¥îâ âਢ¨ «ì®¥ ¯¥à¥á¥ç¥¨¥ (¯® ¥¤¨¨æ¥ £à㯯ë).
DZ®í⮬ã ç¨á«® ᨫ®¢áª¨å p-¯®¤£à㯯 ¢£à㯯¥ Sp à ¢®(p, (p − 1)!) = 1.n(p) = (p − 1)!/(p − 1) = (p − 2)! ᨫã 3-¥¬ â¥®à¥¬ë ¨«®¢ n(p) = (p − 2)! = 1 + pq, q ∈ Z. ¬® ï p − 1, ¯®«ãç ¥¬:(p − 1)! = p − 1 + p(p − 1)q = −1 + p(pq − q + 1) ≡ −1(mod p).9¥ªæ¨ï 10http://mmresource.nm.ru/ 10.29®ªâï¡àï 2002 £. §à¥è¨¬ë¥ £à㯯ë. §¢ ¨¥ í⮣® ª« áá £à㯯 ¢®á室¨â ª í¯®å¥ «ã , ¡¥«ï ¨ ¤à. ¤ ç ® à¥è¥¨¨ «£¥¡à ¨ç¥áª¨å ãà ¢¥¨© ¢ à ¤¨ª « å ¯à¨¢¥« ª ¯®ïâ¨î à §à¥è¨¬®© £à㯯ë. ¯®¬¨¬ ®¯à¥¤¥«¥¨¥ ª®¬¬ãâ â G′ = [G, G] £à㯯ë G: G′ = [G, G] =< [x, y] =−1 −1x y xy|x, y ∈ G >, â. ¥.
ª®¬¬ãâ â — íâ® ¯®¤£à㯯 £à㯯ë G, ¯®à®¤¥ ï ¢á¥¬¨ ª®¬¬ãâ â®à ¬¨.DZ®áª®«ìªã [x, y]−1 = [y, x], ª®¬¬ãâ â G′ ᮢ¯ ¤ ¥â á ᮢ®ªã¯®áâìî ¢á¥å ª®¥çëå ¯à®¨§¢¥¤¥¨© ª®¬¬ãâ â®à®¢. ¥¥ ¬ë ¯®ª § «¨, çâ® ª®¬¬ãâ â G′ — ®à¬ «ì ï ¯®¤£à㯯 £à㯯ë G,¯à¨ í⮬ ä ªâ®à£à㯯 G/G′ = Gab — ¡¥«¥¢ £à㯯 , ®¡« ¤ îé ï á«¥¤ãî騬¨ 㨢¥àá «ìë¬á¢®©á⢮¬ (§¤¥áì π = πG : G → G/G′ — ª ®¨ç¥áª¨© £®¬®¬®à䨧¬, ¯à¨ ª®â®à®¬ π(g) = gG′ ): ¤«ï¢á类£® £®¬®¬®à䨧¬ f ¨§ £à㯯ë G ¢ ¡¥«¥¢ã £à㯯ã A áãé¥áâ¢ã¥â ¨ ¥¤¨áâ¢¥ë© £®¬®¬®à䨧¬f ′ : G/G′ → A, ¤«ï ª®â®à®£® ¤¨ £à ¬¬ ª®¬¬ãâ ⨢ , â. ¥. f = f ′ π:′πG −→ G/G′ = Gabց ↓ ∃!f ′fA®ª § ⥫ìá⢮. ª ª ª ¤«ï x, y ∈ G ¨¬¥¥â f ([x, y]) = [f (x), f (y)] = eA (f — £®¬®¬®à䨧¬£à㯯, A — ª®¬¬ãâ ⨢ ï £à㯯 ), â® f (G′ ) = eA , â. ¥.
G′ = Ker π ⊆ Ker f . DZ®« £ ï f ′ (gG′ ) = f (g),¢¨¤¨¬, çâ®: ) íâ® ®âà ¥¨¥ ®¯à¥¤¥«¥® ª®à४⮠(gG′ = hG′ ⇒ g−1 h ∈ G′ ⇒ f (g−1)f (h) = f (g−1 h) =eA ⇒ f (g) = f (h));¡) f ′ (gG′ hG′ ) = f ′ (ghG′ ) = f (gh) = f (g)f (h) = f ′(gG′ )f ′ (hG′ ) â. ¥. f ′ — £®¬®¬®à䨧¬ £à㯯;¢) ïá®, çâ® f = f ′ π, ¯®áª®«ìªã f ′ π(g) = f ′ (gG′ ) = f (g) ¤«ï ¢á¥å g ∈ G. â® á®®¡à ¥¨¥ —®¤ ¨§ ä®à¬ â¥®à¥¬ë ® £®¬®¬®à䨧¬¥ (⥮६ ® ä ªâ®à¨§ 樨). DZந§¢®¤ë© àï¤ ª®¬¬ãâ ⮢. áᬮâਬ á«¥¤ãî騩 àï¤ ¯®¤£à㯯 £à㯯ë G, §ë¢ ¥¬ë© ¯à®¨§¢®¤ë¬ à冷¬ ª®¬¬ãâ -⮢:(ª ¤ ïG(i−1) ).G ⊇ G′ ⊇ G′′ = [G′ , G′ ] ⊇ .
. . ⊇ G(i) = [G(i−1) , G(i−1) ] ⊇ . . .á«¥¤ãîé ï ¯®¤£à㯯 G(i) ï¥âáï ª®¬¬ãâ ⮬ [G(i−1) , G(i−1) ] ¯à¥¤ë¤ã饩 ¯®¤£àã¯¯ë ¬¥ç ¨¥.¥á«¨ f : G → H — £®¬®¬®à䨧¬ £à㯯, â® f ([x, y]) = [f (x), f (y)], ¨ ¯®í⮬ã f (G′ ) ⊆ H ′ .«¥¤®¢ ⥫ì®, f (G′′ ) ⊆ H ′′ , ¨ ¤ «¥¥ f (G(i) ) ⊆ H (i) ;2) ¥á«¨ f : G → G, f (x) = g −1 xg ¤«ï x ∈ G, — ¢ãâ२© ¢â®¬®à䨧¬, â®, ¯à¨¬¥ïï 1), ¢¨¤¨¬,çâ® g−1 G(i) g ⊆ Gi , â. ¥. Gi ⊳ G (¢á¥ ¯®¤£àã¯¯ë ¯à®¨§¢®¤®£® àï¤ ®à¬ «ìë ¢ G).¯à¥¤¥«¥¨¥.
à㯯 G §ë¢ ¥âáï à §à¥è¨¬®© (ª« áá i), ¥á«¨ G(i) = {e} ¤«ï ¥ª®â®à®£® i. ¬¥ç ¨¥. ᫨ G — ¡¥«¥¢ £à㯯 , â® G′ = {e}.1)¥¬¬ . ᫨ G — à §à¥è¨¬ ï £à㯯 (ª« áá i) ¨ H — ¯®¤£à㯯 £à㯯ë G, â® H — à §à¥è¨¬ ï £à㯯 (ª« áá ¥ ¢ëè¥, 祬 i).®ª § ⥫ìá⢮. ª ª ª G(k) ⊇ H (k) , â® {e} = G(i) ⊇ H (i) â. ¥. H (i) = {e}. ¥¬¬ . ᫨ f : G → H — áîàê¥ªâ¨¢ë© £®¬®¬®à䨧¬ ¨ G — à §à¥è¨¬ ï £à㯯 (ª« áá i), â® H = f (G) — â ª¥ à §à¥è¨¬ ï £à㯯 (ª« áá ¥ ¢ëè¥, 祬 i).®ª § ⥫ìá⢮. ª ª ª f ([x, y]) = [f (x), f (y)] ¨ f — áîàê¥ªâ¨¢ë© £®¬®¬®à䨧¬, â® f (G′ ) =H ′, ¯®í⮬ã H (i) = f (G(i) ) = {eH }.10¥ªæ¨ï 10http://mmresource.nm.ru/«¥¤á⢨¥.
᫨ G — à §à¥è¨¬ ï £à㯯 (ª« áá i) ¨ N ⊳ G, â® ä ªâ®à£à㯯 G/N —à §à¥è¨¬ ï £à㯯 (ª« áá ¥ ¢ëè¥, 祬 i).®ª § ⥫ìá⢮. áᬮâਬ ª ®¨ç¥áª¨© áîàê¥ªâ¨¢ë© £®¬®¬®à䨧¬ πN : G → G/N . ¥®à¥¬ . à㯯 G à §à¥è¨¬ ⮣¤ ¨ ⮫쪮 ⮣¤ , ª®£¤ ¢ £à㯯¥ G áãé¥áâ¢ã¥â á㡮ଠ«ì ï æ¥¯ì ¯®¤£à㯯G = G0 ⊃ G1 ⊃ G2 ⊃ . . .
⊃ Gi−1 ⊃ Gi ⊃ . . . ⊃ Gr = {e}(íâ®®§ ç ¥â, çâ® Gi−1 ⊲ Gi ¤«ï ¢á¥å i) c ¡¥«¥¢ë¬¨ ä ªâ®à£à㯯 ¬¨ Gi−1 /Gi ¤«ï ¢á¥å i.®ª § ⥫ìá⢮.1)®¯ãá⨬, çâ® £à㯯 G à §à¥è¨¬ ï. áᬮâਬ æ¥¯ì ®à¬ «ìëå ¯®¤£à㯯 ª®¬¬ãâ ⮢G ⊃ G′ ⊃ G′′ ⊃ . . . ⊃ G(i) = {e},£¤¥ G(i−1) /G(i) = G(i−1) /[G(i−1) , G(i−1) ] — ¡¥«¥¢ £à㯯 ¤«ï ¢á¥å i.2) ®¯ãá⨬, çâ® áãé¥áâ¢ã¥â 㪠§ ï á㡮ଠ«ì ï æ¥¯ì ¯®¤£à㯯 á ¡¥«¥¢ë¬¨ ä ªâ®à ¬¨. ª ª ª G0 /G1 — ª®¬¬ãâ ⨢ ï £à㯯 , â® G′ ⊆ G1 . «¥¥, G′′ = [G′ , G′ ] ⊆ [G1 , G1 ] ⊆ G2 ,¯®áª®«ìªã G1 /G2 — ¡¥«¥¢ £à㯯 .
ª¨¬ ®¡à §®¬, G(i) ⊆ Gi ¤«ï ¢á¥å i, ¨ ¯®í⮬ã G(r) ⊆ Gr ={e}, â. ¥. G — à §à¥è¨¬ ï £à㯯 (ª« áá ¥ ¢ëè¥, 祬 r). «¥¤á⢨¥. ᫨ N — ®à¬ «ì ï ¯®¤£à㯯 £à㯯ë G, â® G — à §à¥è¨¬ ï £à㯯 ⮣¤ ¨â®«ìª® ⮣¤ , ª®£¤ N ¨ G/N — à §à¥è¨¬ë¥ £à㯯ë.®ª § ⥫ìá⢮. 1) ᫨ G — à §à¥è¨¬ ï £à㯯 , â®, ª ª ¬ë 㥠¤®ª § «¨, N ¨ G/N —à §à¥è¨¬ë¥ £à㯯ë.2) ®¯ãá⨬, çâ® N ¨ G/N = Ḡ à §à¥è¨¬ë¥ £à㯯ë. ®£¤ áãé¥áâ¢ã¥â á㡮ଠ«ìë¥ æ¥¯¨ á ¡¥«¥¢ë¬¨ ä ªâ®à£à㯯 ¬¨ ¡¥«¥¢ë £à㯯ë,G/N = Ḡ = Ḡ0 ⊃ Ḡ1 ⊃ . .