А.В. Михалёв - Лекции по высшей алгебре (1106006), страница 4
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. ⊃ Ḡs = {ē}, Ḡi−1 /Ḡi — ¡¥«¥¢ £à㯯 .N = N0 ⊃ N1 ⊃ . . . ⊇ Nr = {e},Ni−1 /Ni — ᨫ㠮¯¨á ¨ï áâ஥¨ï ¨ ᢮©á⢠¯®¤£à㯯 ä ªâ®à£à㯯ë, Ḡi = Gi /N , N ⊆ Gi ⊆ G, Gi−1 ⊲ Gi,Ḡi−1 /Ḡi = (Gi−1 /N )/(Gi /N ) ∼= Gi−1 /Gi — ¡¥«¥¢ £à㯯 . ª¨¬ ®¡à §®¬, G = G0 ⊃ G1 ⊃ G2 ⊃. . . ⊃ Gs = N = N0 ⊃ N1 ⊃ . .
. ⊃ Nr = {e} — á㡮ଠ«ì ï æ¥¯ì ¢ £à㯯¥ G á ¡¥«¥¢ë¬¨ä ªâ®à£à㯯 ¬¨, â. ¥. G — à §à¥è¨¬ ï £à㯯 . ¥®à¥¬ .®¥ç ï p-£à㯯 G à §à¥è¨¬ (â. ¥., ¥á«¨ |G| = pk , p — ¯à®á⮥ ç¨á«®, k ≥ 1, â®G — à §à¥è¨¬ ï £à㯯 ).®ª § ⥫ìá⢮. DZ஢¥¤ñ¬ ¤®ª § ⥫ìá⢮ ¯® ¨¤ãªæ¨¨. ᨫ㠤®ª § ®£® à ¥¥, Z(G) 6= {e}(â. ¥. æ¥âà p-£àã¯¯ë ¥âਢ¨ «¥). ᨫ㠨¤ãªâ¨¢®£® ¯à¥¤¯®«®¥¨ï ¤«ï £à㯯ë G/Z(G),|G/Z(G)| = pl , l < k, ¢¨¤¨¬, çâ® G/Z(G) — à §à¥è¨¬ ï £à㯯 . â® ¥ ¢à¥¬ï Z(G) — ¡¥«¥¢ £à㯯 , ¨ á«¥¤®¢ â¥«ì® â ª¥ à §à¥è¨¬ . DZ®í⮬ã à §à¥è¨¬ ¨ á ¬ £à㯯 G.
. ®¥ç ï £à㯯 G ï¥âáï ¯àï¬ë¬ ¯à®¨§¢¥¤¥¨¥¬ ᢮¨å ᨫ®¢áª¨å ¯®¤£à㯯 ⮣¤ ¨ ⮫쪮 ⮣¤ , ª®£¤ ¢á¥ ᨫ®¢áª¨¥ ¯®¤£àã¯¯ë ®à¬ «ìë (¢ í⮬ á«ãç ¥ £à㯯 G à §à¥è¨¬ ).. DZãáâì G — ª®¥ç ï £à㯯 , |G| = n = pq, p ¨ q — ¯à®áâë¥ ç¨á« , p < q. ®£¤ G —à §à¥è¨¬ ï £à㯯 .®ª § ⥫ìá⢮. ëç¨á«¨¬ ç¨á«® n(q) q-ᨫ®¢áª¨å ¯®¤£à㯯. áᬮâਬ ¢á¥ ¤¥«¨â¥«¨ ç¨á« n: 1, p, q, pq. ª ª ª p = 0 · q + p, p 6= 1, q ¨ pq — ¤¥«ïâáï q, â®, ¨á¯®«ì§ãï 3-î ⥮६㠨«®¢ , ¢¨¤¨¬, çâ® n(q) = 1. ª¨¬ ®¡à §®¬, áãé¥áâ¢ã¥â ¥¤¨á⢥ ï q-ᨫ®¢áª ï ¯®¤£à㯯 H ¢£à㯯¥ G, |H| = q, á«¥¤®¢ ⥫ì®, ® ®à¬ «ì ¢ G.
ª ª ª G/H ∼= Zp ¨ H ∼= Zq — 横«¨ç¥áª¨¥, á«¥¤®¢ ⥫ì®, ª®¬¬ãâ ⨢ë, ¯®í⮬㠨 à §à¥è¨¬ë¥ £à㯯ë, â® G — â ª¥ à §à¥è¨¬ ï£à㯯 . ¤ ç ¥®à¥¬ 11¥ªæ¨ï 10http://mmresource.nm.ru/ ¤ ç . ᫨ |G| = p2q, q < p, â® G — à §à¥è¨¬ ï£à㯯 .22®ª § ⥫ìá⢮. ¥«¨â¥«¨ ç¨á« n: 1, p, p , q, pq, p q. âáî¤ ïá®, çâ® n(p) = 1, ¨ ¯®í⮬ãáãé¥áâ¢ã¥â ¥¤¨á⢥ ï p-ᨫ®¢áª ï ¯®¤£à㯯 H, |H| = p2 . DZ®í⮬㠮 ®à¬ «ì ¢ £à㯯¥ G,H ⊳ G. ᨫ㠤®ª § ®£® à ¥¥, â ª ª ª |H| = p2 , â® H — ¡¥«¥¢ £à㯯 , ¨ á«¥¤®¢ â¥«ì® —à §à¥è¨¬ ï. «¥¥, |G/H| = q — ¯à®á⮥ ç¨á«®, â.
¥. G/H — 横«¨ç¥áª ï £à㯯 , á«¥¤®¢ ⥫ì®, ¡¥«¥¢ , ¨ â ª¥ à §à¥è¨¬ ï. DZ®í⮬㠨 á ¬ £à㯯 G à §à¥è¨¬ ï. ¥®à¥¬ .à㯯 âà¥ã£®«ìëå¬ âà¨æ G = GTn (K) ¤ ¯®«¥¬ K (â. ¥. âà¥ã£®«ìëå ¬ âà¨æa11 0A=...0a12 . . . a1na22 . . . a2n ¢¨¤ , 0 6= aii ∈ K) ï¥âáï à §à¥è¨¬®© £à㯯®©.... ... ...0 .
. . ann®ª § ⥫ìá⢮. 1) áᬮâਬ ã¨âà¥ã£®«ìãî ¯®¤£à㯯ã H = U Tn (K) ¬ âà¨æ ¢¨¤ B =1∗ ... ∗1 ... ∗ 0. DZਠ㬮¥¨¨ âà¥ã£®«ìëå ¬ âà¨æ ¨å ᮮ⢥âáâ¢ãî騥 ¤¨ £® «ìë¥... ... ... ...00 ... 1í«¥¬¥âë ¯¥à¥¬® îâáï, ¯®í⮬㠢 ¬ âà¨æ¥ A−1 BA (i, i)-®¬ ¬¥á⥠á⮨â a−1ii 1aii = 1, â. ¥.A−1 BA ∈ H, ¨ ¯®í⮬ã H — ®à¬ «ì ï ¯®¤£à㯯 ¢ G, H ⊳ G. â® ¥ á®®¡à ¥¨¥ ¯®ª §ë¢ ¥â,çâ® [G, G] ⊆ H, ¯®áª®«ìªã ¤«ï A, D ∈ GTn (K) ¢ ª®¬¬ãâ â®à¥ [A, D] ¬¥á⥠(i, i) á⮨â í«¥¬¥â−1a−1ii dii aii dii = 1, â. ¥. [A, D] ∈ H. DZ®í⮬ã ä ªâ®à£à㯯 G/H — ¡¥«¥¢ , ¨ á«¥¤®¢ ⥫ì®,à §à¥è¨¬ ï.2) ®ª ¥¬ ¨¤ãªæ¨¥© ¯® n, çâ® H = Hn — à §à¥è¨¬ ï £à㯯 . áᬮâਬ ®â®¡à ¥¨¥fB′∗b n−1 , B ′ , C ′ ∈ U Tn−1 (K), â® f (B) = B ′ .
ª ª ª ¤«ï x, y ∈ K0...0 1 ′ ′B′xC′yBCB′y + x=,0...0 10...0 10...01En−1 x n−1bâ® f — áîàê¥ªâ¨¢ë© £®¬®¬®à䨧¬ £à㯯, ¯à¨ í⮬ Ker f =x∈K. ®£¤ 01Ker f ⊳ U Tn (K) (ª ª ï¤à® £®¬®¬®à䨧¬ f ) ¨¯à¨ ª®â®à®¬ ¥á«¨ B =¨¬¥¥¬Hn = U Tn (K) → U Tn−1 (K) = Hn−1 ,U Tn (K)/ Ker f ∼= U Tn−1 (K)(¢á¨«ã â¥®à¥¬ë ® £®¬®¬®à䨧¬¥). ® Ker f — ¡¥«¥¢ £à㯯 , ¨ á«¥¤®¢ â¥«ì® — à §à¥è¨¬ ï£à㯯 . DZ® ¨¤ãªâ¨¢®¬ã ¯à¥¤¯®«®¥¨î, U Tn−1(K) — à §à¥è¨¬ ï £à㯯 . ®£¤ ¨ £à㯯 H = Hn — à §à¥è¨¬ ï.3) ª ª ª H = U Tn (K) — à §à¥è¨¬ ï £à㯯 ¨ G/H — à §à¥è¨¬ ï £à㯯 , â® G = GTn (K) —à §à¥è¨¬ ï £à㯯 .12¥ªæ¨ï 11http://mmresource.nm.ru/ 11.5ëç¨á«¥¨ï ¢ £à㯯¥ ¯®¤áâ ®¢®ª Sn. 1-®¬ ᥬ¥áâॠ¬ë à áᬮâ५¨ £à㯯㠯®¤áâ ®¢®ª Sn á § ¯¨áìîσ(τ (i)), â. ¥.
à áᬠâਢ ï «¥¢ë© ¯®«¨£® Sn {1, 2, . . . , n}. ¬¥â¨¬, çâ®:(i1 , i2 , . . . , ik ) = (i1 , ik )(i1 , ik−1 ) . . . (i1 , i2 )(¢®ï¡àï 2002 £.㬮¥¨ï á«¥¢ (στ )(i) =ç áâ®áâ¨, (1, 2, . . . , k) = (1, k)(1, k − 1) . . . (1, 2)); (i, j) = (1, i)(1, j)(1, i) ¤«ï 1 6= i, 1 6= j. ¬ ¡ã¤ãâ ¯®«¥§ë à §ë¥ á¨áâ¥¬ë ®¡à §ãîé¨å £à㯯ë Sn :Sn =< (i, j), i 6= j >=< (1, 2), (1, 3), . .
. , (1, n) > .¥¬¬ .®¯à泌¥ ¢ £à㯯¥ Sn.τ (1, 2, . . . , k)τ −1 = (τ (1), . . . , τ (k)) (τ −1 (1, 2, . . . , k)τ = (τ −1 (1), . . . , τ −1 (k)).®ª § ⥫ìá⢮. ᫨ σ(i) = j, τ (i) = s, τ (j) = t, â® (τ στ −1 )(s) = (τ στ −1 )(τ (i)) = (τ σ)(i) =τ (j) = t. . ¢¥ ¯®¤áâ ®¢ª¨ σ, γ ∈ Sn ᮯàï¥ë ⮣¤ ¨ ⮫쪮 ⮣¤ , ª®£¤ ®¨ ¨¬¥îâ ®¤¨ ª®¢®¥ 横«®¢®¥ à §«®¥¨¥.®ª § ⥫ìá⢮.1) ᫨ γ = τ στ −1 ¨ σ = σ1 . . . σr — à §«®¥¨¥ ¯®¤áâ ®¢ª¨ σ ¢ ¯à®¨§¢¥¤¥¨¥ 横«®¢ á ¥¯¥à¥á¥ª î騬¨áï ®à¡¨â ¬¨, ⮥®à¥¬ γ = (τ σ1 τ −1 )(τ σ2 τ −1 ) . .
. (τ σr τ −1 ),{τ σi τ −1 } —横«ë, ®à¡¨âë ª®â®àëå ïîâáï ®¡à § ¬¨ ®à¡¨â 横«®¢ σi , ¨ ¯®í⮬ã í⨠®à¡¨âë ¤ îâ à §¡¨¥¨¥ ¬®¥á⢠{1, 2, . . . , n}. ª¨¬ ®¡à §®¬, ¯®¤áâ ®¢ª¨ γ ¨ σ ¨¬¥îâ ®¤¨ ª®¢ë¥ 横«®¢ë¥à §«®¥¨ï.2) ᫨ γ ¨ σ ¨¬¥îâ ®¤¨ ª®¢®¥ 横«®¢®¥ à §«®¥¨¥, ⮠ᮮ⢥âá⢨¥ ¬¥¤ã í«¥¬¥â ¬¨ ᮮ⢥âáâ¢ãîé¨å ®à¡¨â ¯à¨¢®¤¨â á ª ¡¨¥ªæ¨¨ τ , â. ¥. σ ∈ Sn , ¤«ï ª®â®à®© γ = τ στ −1 .«¥¤á⢨¥. ¨á«® ª« áᮢ ᮯàïñëå í«¥¬¥â®¢ £à㯯ë Sn ᮢ¯ ¤ ¥â á ç¨á«®¬ ρn à §¡¨¥¨© ç¨á« n ¢ ¢¨¤¥n = n1 + n2 + .
. . + nr ,0 < n1 ≤ n2 ≤ . . . ≤ nr .®ª § ⥫ìá⢮. DZ®¤áâ ®¢ª σ ¯à¥¤áâ ¢«ï¥âáï ®¤®§ ç® ¢ 横«®¢®¬ à §«®¥¨¨ n1 -横« ,n2 -横« , . . ., nr -横« , £¤¥ 0 < n1 ≤ n2 ≤ . . . ≤ nr , ¥© ᮯ®áâ ¢«ï¥âáï à §¡¨¥¨¥n = n1 + n2 + . . . + nr .DZਬ¥à.
ρ(1) = 1, ρ(2) = 2, ρ(3) = 3, ρ(4) = 5(2 = 2, 2 = 1 + 1; 3 = 3, 3 = 1 + 2, 3 = 1 + 1 + 1; 4 = 4, 4 = 1 + 3, 4 = 1 + 1 + 2, 4 = 1 + 1 + 1 + 1,4 = 2 + 2).(Sn ).1) Z(S2 ) = S2 ; Z(Sn ) = {e} ¯à¨ n ≥ 3;2) Z(A3 ) = A3 ; Z(An ) = {e} ¯à¨ n ≥ 4.®ª § ⥫ìá⢮.1) ᫨ e 6= σ ∈ Sn ¯à¨ n ≥ 3, â® ¯ãáâì j = σ(i) 6= i ¨ k ∈/ {i, j}.
®£¤ [(jk)σ(jk)−1 ](i) = k 6= j =−1σ(i), â. ¥. (jk)σ(jk) 6= σ, (jk)σ 6= σ(jk), ¨â ª, σ ∈/ Z(Sn ).¥®à¥¬ ® æ¥âॠ£àã¯¯ë ¯®¤áâ ®¢®ª13¥ªæ¨ï 11http://mmresource.nm.ru/2) DZãáâì e 6= σ ∈ An , n ≥ 4, j = σ(i) 6= i, k, l ∈/ {i, j}, k 6= l. ®£¤ [(jkl)σ(jkl)−1 ](i) = k 6= j = σ(i),â. ¥. (jkl)σ 6= σ(jkl), (jkl) ∈ An , ¨â ª σ ∈/ Z(An ).. «ï 横«®¢ ¤«¨ë 2 τ1 , τ2 (â.
¥. ¤«ï âà ᯮ§¨æ¨©) £à㯯ë Sn ¯à¨ n ≥ 3 ¯à®¨§¢¥¤¥¨¥τ1 τ2 «¨¡® 3-横«, ¯à®¨§¢¥¤¥¨¥ ¤¢ãå 3-横«®¢.®ª § ⥫ìá⢮.«ãç © 1: ᫨ τ1 = τ2 , â®τ1 τ2 = τ12 = e = (ijk)(kji).¥¬¬ «ãç © 2:2 )τ1 6= τ2 .®à¡¨âë ¯¥à¥á¥ª îâáï (¯® ®¤®¬ã í«¥¬¥âã i):(i, k)(i, l) = (ilk),§¤¥áì k 6= l.2¡) ࡨâë âà ᯮ§¨æ¨© τ1 ¨ τ2 ¥ ¯¥à¥á¥ª îâáï:(ij)(kl) = (ilj)(ilk).¥®à¥¬ .An =< {(ijk)} >=< (123), (124), . . .
, (12n) >®ª § ⥫ìá⢮.¯à¨ n ≥ 3.1) ᫨ σ ∈ An , n ≥ 3, â® σ = τ1 . . . τ2m , £¤¥ τi — âà ᯮ§¨æ¨ï (横«τ2i−1 τ2i — ¨«¨ 3-横«, ¨«¨ ¯à®¨§¢¥¤¥¨¥ ¤¢ãå 3-横«®¢, ⮤«¨ë2). ª ª ªAn =< {(i, j, k)} > .2)(i, j, k) =(1, 2, i)(2, j, k)(1, 2, i)−1 ;(2, j, k) =(1, 2, j)(1, 2, k)(1, 2, j)−1 ;(1, j, k) =(1, 2, k)−1 (1, 2, j)(1, 2, k).¥®à¥¬ .1) [S2 , S2 ] = {e}; [Sn , Sn ] = An ¯à¨ n ≥ 3.2) [A3 , A3 ] = {e};[A4 , A4 ] = V4 = {e, (1, 2)(3, 4), (1, 3)(2, 4), (1, 4)(2, 3)};[An , An ] = An ¯à¨ n ≥ 5.®ª § ⥫ìá⢮.1) ª ª ª [a, b] = a−1 b−1 ab ¤«ï a, b ∈ Sn ¢á¥£¤ ï¥âáï çñ⮩ ¯®¤áâ ®¢ª®©, â® [Sn , Sn ] ⊆ An . ª ª ª An =< {(i, j, k)} > ¨(i, j, k) = (i, j)(i, k)(i, j)(i, k) = [(i, j), (i, k)],â® An ⊆ [Sn , Sn ].2) ) á®, çâ® [A3 , A3 ] = {e} (A3 — ¡¥«¥¢ £à㯯 , |A3 | = 2).¡) ª ª ª[(i, j, k), (i, j, l)] = (k, j, i)(l, j, i)(i, j, k)(i, j, l) = (i, j)(k, l),[(i, j, k), (i, l, j)] = (k, j, i)(j, l, i)(i, j, k)(i, l, j) = (i, k)(j, l),â® V4 ⊆ [A4 , A4 ].14¥ªæ¨ï 11http://mmresource.nm.ru/ ª ª ª |A4 /V4 | = 12/4 = 3, â® A4 /V4 — ¡¥«¥¢ £à㯯 , ¯®í⮬ã [A4 , A4 ] ⊆ V4 .
â ª, [A4 , A4 ] =V4 .¢) DZਠn ≥ 5 ¤«ï {i, j, k} ©¤ãâáï l, m ∈/ {i, j, k}, l 6= m. DZ®í⮬ã(i, j, k) = (i, j, m)(i, k, l)(m, j, i)(l, k, i) = [(m, j, i), (l, k, i)],â ª¨¬ ®¡à §®¬, An ⊆ [An , An ] ¨ á«¥¤®¢ ⥫ì®, An = [An , An ] ¯à¨ n ≥ 5. ¬¥ç ¨¥.1) § ªà¨â¥à¨ï ᮯàïñ®áâ¨ í«¥¬¥â®¢ ¢ S4 ïá®, çâ® ç¥â¢¥à ï £à㯯 «¥© V4 ={e, (1, 2)(3, 4), (1, 3)(2, 4), (1, 4)(2, 3)} ®à¬ «ì ¢ S4 , â. ¥. V4 ⊳ S4 . â ª, S3 , V4 — ¯®¤£à㯯 .2) ª ª ª ¥¥¤¨¨çë¥ í«¥¬¥âë ¨§ V4 ¥ ®áâ ¢«ïîâ í«¥¬¥â 4 ¬¥áâ¥, â® S3 ∩ V4 = {e},|S3 V4 | = |S3 ||V4 | = 6 · 4 = 24. DZ®í⮬ã S3 V4 = S4 . DZ® ¢â®à®© ⥮६¥ ® £®¬®¬®à䨧¬¥:S4 /V4 = S3 V4 /V4 ∼= S3 /S3 ∩ V4 ∼= S3 .îàê¥ªâ¨¢ë© £®¬®¬®à䨧¬ S4 → S3 á ï¤à®¬ V4 ¨¬¥¥â ¯à®§à çë© £¥®¬¥âà¨ç¥áª¨© á¬ëá« £®¬®¬®à䨧¬ ¨§ £àã¯¯ë ¤¢¨¥¨© ªã¡ £à㯯㠤¢¨¥¨ï ¢¯¨á ®£® ¢ ¥£® â¥âà í¤à .¯à ¥¨¥.
DZãáâì K — ¯®«¥, n ≥ s. ®£¤ :1) [GLn (K), GLn (K)] = SLn (K);2) [SLn (K), SLn (K)] = SLn (K).DZà®áâë¥ £à㯯ë.à㯯 G §ë¢ ¥âáï ¯à®á⮩, ¥á«¨ ã ¥ñ ¥â ®à¬ «ìëå ¯®¤£à㯯 N¨ G.⊳ G,®â«¨çëå ®â {e} ¬¥ç ¨¥ 1. DZà®áâë¥ ¡¥«¥¢ë £àã¯¯ë — íâ®, ¢ â®ç®áâ¨, 横«¨ç¥áª¨¥ £àã¯¯ë ¯à®á⮣® ¯®à浪 . ¥©á⢨⥫ì®, ¢ ¡¥«¥¢®© £à㯯¥ «î¡ ï ¯®¤£à㯯 ®à¬ «ì . DZ®í⮬ã, ¯à®áâ ï ¡¥«¥¢ £à㯯 ï¥âáï æ¨ª«¨ç¥áª®©. £à㯯¥ Z ¬®£® ¯®¤£à㯯, ¢ ç áâ®áâ¨, 2Z, â. ¥. ® ¥ ï¥âáï¯à®á⮩. ᫨ G = (a), O(a) = n = kl, â® (ak ) ⊂ (a), ¨ £à㯯 G ¥ ï¥âáï ¯à®á⮩.