В.А. Артамонов - Лекции по алгебре, 3 семестр, мех-мат МГУ (1106002), страница 3
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áᬮâਬ ¬®¦¥á⢮ X = {gP |g ∈ G} «¥¢ëå ᬥ¦ëå ª« áᮢ G ¯® P .à㯯 Γ ¤¥©áâ¢ã¥â X «¥¢ë¬¨ ᤢ¨£ ¬¨, â. ¥. ¥á«¨ y ∈ Γ, â® y(gP ) = (yg)P . ®ká«¥¤á⢨î 1.58 ¯®à冷ª «î¡®© ®à¡¨âë | OrbgP | ¤¥«¨â |Γ| = p , k ≤ n. «¥¤®¢ ⥫ì®, ¥á«¨n|G| = p m, £¤¥ (p, m) = 1, â®X|G| X=| OrbgP | =pki .m=|P |g(p, m) = 1, â® ¯®à冷ª ¥ª®â®à®© ®à¡¨âë OrbgP à ¢¥ 1, â. ¥. ΓgP = gP . âáî¤ g −1 Γg ⊆ P ¨ Γ ⊆ gP g −1 . ¬¥â¨¬, çâ® gP g −1 ' P ï¥âáï ᨫ®¢áª®© p-¯®¤£à㯯®©. −1ç áâ®áâ¨, ¥á«¨ Γ { ᨫ®¢áª ï p-¯®¤£à㯯 , â® Γ = gP g. ª ª ª¥®à¥¬ 1.77 (à¥âìï ⥮६ ¨«®¢ ). ãáâì Np { ç¨á«® ᨫ®¢áª¨å p-¯®¤£à㯯 ¢G.
®£¤ Np ¤¥«¨â ¯®à冷ª £à㯯ë G ¨ Np ≡ 1 mod p.®ª § ⥫ìá⢮. ãáâìᬮâਬ ¤¥©á⢨¥G SS®à¡¨âë, ¯à¨ç¥¬ ¯® á«¥¤á⢨î 1.58 ¯®à冷ª í⮩ ®à¡¨âë,¯ëp-¯®¤£à㯯 £à㯯ë G. áS á®á⮨⠨§ ®¤®©à ¢ë© Np , ¤¥«¨â ¯®à冷ª £àã¯-{ ¬®¦¥á⢮ ¢á¥å ᨫ®¢áª¨åᮯà殮¨ï¬¨.
® ¢â®à®© ⥮६¥ ¨«®¢ G.ãáâìS = {P0 , . . . , Pr }. áᬮâਬ ¤¥©á⢨¥P0 Sᮯà殮¨ï¬¨. ®£¤ ¢ ¥âáï ¥¯¥à¥á¥ª î騥áï ®à¡¨âë, ¤«¨ ª ¦¤®© ¨§ ª®â®àëå à ¢ á⥯¥¨P0 , ¨ ¯®í⮬ã r = pe1 + · · · + pes .|S| = 1 + r ≡ 1 mod p.®à¡¨â ᮢ¯ ¤ ¥â á®âªã¤ ᫨ei > 0¤«ï ¢á¥åp.i > 0,Sà §¡¨-¤ ¨§â®r = lp,141. e1 = 0, â. ¥. ®à¡¨â P1gP1 g −1 = P1 ¤«ï ¢á¥å g ∈ P0 . ® ⮣¤ P0 P1ª ª P0 , â ª ¨ P1 , â.
¥. P0 = P0 P1 = P1 .।¯®«®¦¨¬, çâ®, ¯à¨¬¥à,®§ ç ¥â, çâ®á®¤¥à¦ 饩⠪¦¥ ®¤®í«¥¬¥â .ï¥âáïâ®p-¯®¤£à㯯®©¢G,6. à®áâë¥ £à㯯ë¯à¥¤¥«¥¨¥ 1.78. ¥ ¡¥«¥¢ £à㯯 ®à¬ «ìë¥ ¯®¤£à㯯륮६ 1.79.GG §ë¢ ¥âáï¯à®á⮩,¥á«¨ ¢ ¥© ⮫쪮 ¤¢¥¨ 1.à㯯 A5 ¯à®áâ .®ª § ⥫ìá⢮. ¬ ¯®âॡã¥âáï ¥áª®«ìª® «¥¬¬.¥¬¬ 1.80. ª 横« ®ª § ⥫ìá⢮.(i1 , . .
. , ik ) ∈ Sn à ¢¥ (−1)k−1 .(i1 , . . . , ik ) = (i1 , ik )(i1 , ik−1 ) · · · (i1 , i3 )(i1 , i2 ).0¥¬¬ 1.81. ãáâì σ ∈ An ¨ Orbσ , Orbσ { ª« ááë ᮯà殮ëå í«¥¬¥â®¢0¨ An . ®£¤ «¨¡® Orbσ = Orbσ , «¨¡®σ ¢ Sn| Orbσ |.2®ª § ⥫ìá⢮. ãáâì τ ∈ C(σ) \ An , £¤¥ C(σ) { æ¥âà «¨§ â®à σ ¢ Sn . ᫨γ ∈ C(σ) \ An , â® τ −1 γ ∈ C(σ) ∩ An . «¥¤®¢ ⥫ì®, ¯®«ãç ¥¬ à §¡¨¥¨¥ C(σ) ¤¢ | Orb0σ | =«¥¢ëå ᬥ¦ëå ª« áá ¯® ¯®¤£à㯯¥C(σ) ∩ An .| Orbσ | = ᫨ ¦¥C(σ) = τ [C(σ) ∩ An ] ∪ [C(σ) ∩ An ]âáî¤ |C(σ)| = 2|C(σ) ∩ An |, ¨ ¯®í⮬ãC(σ) ⊆ An ,|Sn |n!|An |=== | Orb0σ |.|C(σ)|2|C(σ) ∩ An ||C(σ) ∩ An |C(σ) = C(σ) ∩ An ,â®| Orbσ | =®âªã¤ n!2|An ||Sn |=== 2| Orb0σ |.|C(σ)||C(σ) ∩ An ||C(σ) ∩ An |¥¬¬ 1.82.ᥠâà®©ë¥ æ¨ª«ë ®¡à §ãîâ ®¤¨ ª« áá ᮯà殮ëå í«¥¬¥â®¢ ¢An , n ≥ 5.®ª § ⥫ìá⢮.
áᬮâਬ ª« áá ᮯà殮ëå ¢âன®© 横«(i, j, k). ᫨l 6= m ∈/ {i, j, k},Aní«¥¬¥â®¢, ᮤ¥à¦ 騩â®(k, l, m)(i, j, k)(k, l, m)−1 = (i, j, l).âáî¤ ¢ë⥪ ¥â ã⢥ত¥¨¥ «¥¬¬ë. ¢¥à訬 ¤®ª § ⥫ìá⢮ ⥮६ë.¦¥ëå í«¥¬¥â®¢ ¢A5 .ᥠâà®©ë¥ æ¨ª«ë ®¡à §ãîâ ®¤¨ ª« áá ᮯàï-â®â ª« áá ¨¬¥¥¬ ¯®à冷ª 55!5!2=2== 20,32!3!3!¯®áª®«ìªã(i, j, k), (j, i, k){ ¥¤¨áâ¢¥ë¥ æ¨ª«ë, ¯®áâà®¥ë¥ âà¥å í«¥¬¥â åi, j, k . «¥¥(j, k, l)(i, j)(k, l)(j, k, l)−1 = (i, k)(j, l);(j, k, m)(i, j)(k, l)(j, k, m)−1 = (i, k)(j, m).«¥¤®¢ ⥫ì®, ¢á¥ ¯à®¨§¢¥¤¥¨ï ¤¢®©ëå æ¨ª«®¢3 × 5 = 15í«¥¬¥â®¢ ¢A5 .{(i, j)(k, l)}®¡à §ãîâ ®¤¨ ª« áá ¨§6. 15(1, 2, 3, 4, 5) = π(1, 2, 3, 5, 4)π −1 , £¤¥ π ∈ Sn , â®π ¬®¦® § ¬¥¨âì «î¡®© í«¥¬¥â π(1, 2, 3, 5, 4)m , m ≥ 0. «¥¤®¢ ⥫ì®, ¬®¦® áç¨â âì, çâ® π(1) = 1.
®£¤ ¯® ¯à¥¤«®¦¥¨î 1.67 (1, 2, 3, 4, 5) = (1, π(2), π(3), π(5), π(4)),â.¥.π(2) = 2, π(3) = 3, π(5) = 4, π(4) = 5. â ª, π = (4, 5) ∈/ A5 . ª¨¬ ®¡à §®¬,(1, 2, 3, 4, 5), (1, 2, 3, 5, 4) «¥¦ â ¢ à §ëå ª« áá å ᮯà殮ëå í«¥¬¥â®¢ ¢ A5 . ® «¥¬¬¥ 1.81 ¨¬¥¥âáï ¤¢ ª« áá ᮯà殮ëå í«¥¬¥â®¢, á®áâ®ïé¨å ¨§ 横«®¢ ¤«¨ë 5 ¢ A5 . áᬮâਬ ª« áá{(1,2,3,4,5)}. ᫨¡ ª« áá ᮤ¥à¦ â ¯® 1 5!4!24=== 122 522í«¥¬¥â®¢.
¥©á⢨⥫ì®, ¯à¨ ¯®¤áç¥â¥ ç¨á« 横«®¢ (i1 , . . . , i5 )« £ âì, çâ® i1 = 1. «ï i2 , i3 , i4 , i5 ®áâ ¥âáï 4! ¢ ਠ⮢.¤«¨ë 5 ¬®¦® ¯à¥¤¯®-â ª, ¨¬¥¥¬ à §¡¨¥¨¥ ª« ááë ᮯà殮ëå í«¥¬¥â®¢A5 = {1}1 + {(1, 2, 3)}20 + {(1, 2)(3, 4)}15 + {(1, 2, 3, 4, 5)}12 + {(1, 2, 3, 5, 4)}12 .ãáâìN / A5 .®£¤ Nᮤ¥à¦¨â 楫¨ª®¬ ¥ª®â®àë¥ ª« ááë ᮯà殮ëå í«¥¬¥â®¢.®í⮬ã|N | = 1 + 20n2 + 15n3 + 12n4 + 12n5 ,¨|N |¤¥«¨â60 = |A5 |.£¤¥ ¤¨áâ¢¥ë¥ ¢ ਠâë: «¨¡® ¢á¥ni = 0, 1,ni = 0,«¨¡® ¢á¥ni = 1.§«®¦¨¬ ¤à㣮¥ ¤®ª § ⥫ìá⢮ ¡®«¥¥ ®¡é¥© ⥮६ë.¥®à¥¬ 1.83.à㯯ëAn , n ≥ 5, ¯à®áâ뮪 § ⥫ìá⢮. ¬ ¯®âॡã¥âáï ¥áª®«ìª® «¥¬¬.¥¬¬ 1.84.à㯯 An ¯®à®¦¤ ¥âáï âன묨 横« ¬¨.®ª § ⥫ìá⢮. ᫨ ¨¤¥ªáëi, j, k, là §«¨çë, â®(i, j)(k, l) = (i, j, k)(j, k, l),(i, j)(j, k) = (i, j, k).¥¬¬ 1.85.¨ãáâìN / An ᮤ¥à¦¨â âன®© 横«.
®£¤ N = An .®ª § ⥫ìá⢮. ãáâì(i, j, k) ∈ N(a, b, c) ∈ An .¨ ª ª ªn ≥ 5,â® áãé¥áâ¢ã¥ââ ª ï ¯®¤áâ ®¢ª σ=£¤¥(u, v) = (u0 , v 0 )¨«¨iajb(u, v) = (v 0 , u0 ),kcçâ®uu0vv0...∈ An ,...σ(i, j, k)σ −1 = (a, b, c).áâ ¥âáï ¢®á¯®«ì§®¢ âì-áï ¯à¥¤ë¤ã饩 «¥¬¬®©.¥¬¬ 1.86.
ãáâì N ᮤ¥à¦¨â ¯®¤áâ ®¢ªã σ , ¢ à §«®¦¥¨¨ ª®â®à®© ¥§ ¢¨á¨¬ë¥ 横«ë ¨¬¥¥âáï æ¨ª« ¤«¨ë ¥ ¬¥ìè¥ 4. ®£¤ N = An .®ª § ⥫ìá⢮. ãáâìσ = (i, j, k, l, . . .) · · · .®£¤ −1 −1τ = (i, j, k)σ(i, j, k)σNᮤ¥à¦¨â í«¥¬¥â= (i, j, l).áâ ¥âáï ¢®á¯®«ì§®¢ âìáï ¯à¥¤ë¤ã饩 «¥¬¬®©.¥¬¬ 1.87. ãáâì N ᮤ¥à¦¨â ¯®¤áâ ®¢ªã σ , ¢ à §«®¦¥¨¨ ª®â®à®© ¥§ ¢¨á¨¬ë¥ 横«ë ¨¬¥îâáï ¥ ¬¥¥¥ ¤¢ãå æ¨ª«®¢ ¤«¨ë 3. ®£¤ N = An .®ª § ⥫ìá⢮. ãáâìσ = (i, j, k)(a, b, c) · · · .0−1 −1σ = (k, a, b)σ(k, a, b)âáî¤ N = An¯® ¯à¥¤ë¤ã饩 «¥¬¬¥.󮣤 ¢Nᮤ¥à¦¨âáï= (i, c, k, a, b).161.
â ª, ¬®¦® áç¨â âì, çâ®Nᮤ¥à¦¨â ¯®¤áâ ®¢ªãσ,¢ à §«®¦¥¨¥ ª®â®à®© ¢ ¥§ -¢¨á¨¬ë¥ 横«ë ¥ ¡®«¥¥ ®¤®£® 横« ¤«¨ë 3, ¯à¨ç¥¬ ®áâ «ìë¥ æ¨ª«ë ¨¬¥îâ ¤«¨ã 2.σ 2 ∈ N ï¥âáï âà®©ë¬ æ¨ª«®¬, ¨ ⮣¤ N = An .çâ® σ ï¥âáï ¯à®¨§¢¥¤¥¨¥¬ ç¥â®£® ç¨á« ¥§ ¢¨- ᫨ ¨¬¥¥âáï ®¤¨ âன®© 横«, â® ª¨¬ ®¡à §®¬, ¬®¦® áç¨â âì,ᨬëå æ¨ª«®¢ ¤«¨ë 2.ãáâìσ = (i, j)(a, b). ᫨c∈/ {i, j, a, b},â®−1(i, j, c)σ(i, j, c)N = An .σ = (i, j)(a, b)(i0 , j 0 )(a0 , b0 ) · · · .Nᮤ¥à¦¨âσ = (i, c, j),®âªã¤ , ª ª ¨ ¢ëè¥ãáâì ⥯¥àì0®£¤ 0Nᮤ¥à¦¨â ¨0(j, a)(b, i )σ(b, i )(j, a)σ = (i, i , b)(j, a, j 0 ). ª ¨ ¢ëè¥ ®âáî¤ á«¥¤ã¥â ã⢥ত¥¨¥ ⥮६ë.7.
§à¥è¨¬ë¥ £à㯯ëx, y { í«¥¬¥âë[x, y] = xyx−1 y −1 .¯à¥¤¥«¥¨¥ 1.88. ãáâì §ë¢ ¥âáï í«¥¬¥â£à㯯ëG. ®¬¬ãâ â®à®¬í«¥¬¥â®¢x, y¯à ¦¥¨¥ 1.89. ®ª § âì, çâ®[x, y]−1 = [y, x],¨z[x, y]z −1 = [zxz −1 , zyz −1 ].ਬ¥àë 1.90. ®ª § âì, çâ®Sn [(i, j), (j, k)] = (i, j, k), ¥á«¨ ¨¤¥ªáë i, j, k à §«¨çë;GL(n, k), £¤¥ k { ª®«ìæ®, [1 + aEik , 1 + bEkj ] = 1 + abEij , ¥á«¨(1) ¢ £à㯯¥ ¯¥à¥áâ ®¢®ª(2) ¢ £à㯯¥ ¬ âà¨æ¨¤¥ªáëi, j, kà §«¨çë.®¬¬ãâ ⮬¯à¥¤¥«¥¨¥ 1.91.¤¥¨© ª®¬¬ãâ â®à®¢ ¢G0 = [G, G] §ë¢ ¥âáï ¬®¦¥á⢮ ¢á¥å ¯à®¨§¢¥-G.।«®¦¥¨¥ 1.92.G0 / G . ᫨ N / G, â® á«¥¤ãî騥 ãá«®¢¨ï íª¢¨¢ «¥âë:G/N { ¡¥«¥¢ ;।«®¦¥¨¥ 1.93.(1)£à㯯ë(2)N ⊇ G0 .¥®à¥¬ 1.94.Sn0 = An .®ª § ⥫ìá⢮.
㦮 ¢®á¯®«ì§®¢ âìáï «¥¬¬®© 1.84 ¨ ¯à¨¬¥à®¬ 1.90.¥®à¥¬ 1.95. ᫨n ≥ 3, ¨ k { ¯®«¥, â® GL(n, k)0 = SL(n, k)0 = SL(n, k).¯à ¦¥¨¥ 1.96. ®ª § âì, çâ®k ᮤ¥à¦¨â ¥ ¬¥¥¥ ç¥âëà¥å í«¥¬¥â®¢, â® GL(2, k)0 = SL(2, k); ¨¬¥®,∗áãé¥áâ¢ã¥â â ª®© í«¥¬¥â q, q − 1 ∈ k , â® q 01 (q − 1)−1 a,= 1 + aE12 ;0 101(1) ¥á«¨ ¯®«¥¥á«¨(2)GL(2, F2 ) ' S3 ,¨ ¯®í⮬ãGL(2, F2 )0 6= SL(2, F2 ) = GL(2, F2 ).¯à ¦¥¨¥ 1.97. ëç¨á«¨âìਬ¥àë 1.98.A04 = V4 ,¨¯à¥¤¥«¥¨¥ 1.99. ᫨à㯯 GGL(2, F3 )0 .A0n = An ,G¥á«¨n ≥ 5.{ £à㯯 , â® ¯®«®¦¨¬à §à¥è¨¬ ¥á«¨ áãé¥áâ¢ã¥â â ª®¥ âãà «ì®¥ ¬¥ç ¨¥ 1.100. «ï «î¡ëåm, n > 0G(1) = G0 ¨G(k+1) = [Gk , Gk ].(m)ç¨á«® m, çâ® G= 1.¢¥à® à ¢¥á⢮(G(n) )(m) = G(n+m) .7. ãáâì।«®¦¥¨¥ 1.101.17f : G → H { £®¬®¬®à䨧¬ £à㯯.
®£¤ f (G(k) ) ⊆ H (k) .f { áîàꥪ⨢®, â® f (G(k) ) = H (k) . ᫨¯à ¦¥¨¥ 1.102. ®ª § âì, çâ®(1) ¥á«¨(2)H{ ¯®¤£à㯯 ¢ £à㯯¥k;G(k) / G(2)£à㯯ë£à㯯ëâ®H (k) ⊆ G(k)¤«ï «î¡®£® âãà «ì®£® ç¨á« ãáâì।«®¦¥¨¥ 1.103.(1)G,¤«ï «î¡®£® âãà «ì®£® ç¨á« k.N / G. «¥¤ãî騥 ãá«®¢¨ï íª¢¨¢ «¥âë:G à §à¥è¨¬ ;G/N, ¨ N à §à¥è¨¬ë.®ª § ⥫ìá⢮. ®á¯®«ì§®¢ âìáï¯à¥¤«®¦¥¨¥¬ 1.101«ï £à㯯ë।«®¦¥¨¥ 1.104.(1)(2)G á«¥¤ãî騥 ãá«®¢¨ï íª¢¨¢ «¥âë:£à㯯ë G à §à¥è¨¬ ;áãé¥áâ¢ã¥â â ª®© àï¤ ¯®¤£à㯯ëG = G0 ⊃ G1 ⊃ · · · ⊃ Gk−1 ⊃ Gk = 1,çâ®Gi+1 / Gi ¨ Gi /Gi+1 { ¡¥«¥¢® ¤«ï ¢á¥å i.®ª § ⥫ìá⢮. 㦮 ¢®á¯®«ì§®¢ âìáï ¯à¥¤«®¦¥¨¥¬ 1.103 ¨ ¨¤ãªæ¨¥© ¯®ã¡¥¤¨¢è¨áì, çâ® £à㯯 «¥¤á⢨¥ 1.105.G1à §à¥è¨¬ .ãáâìp-¯à®á⮥ ç¨á«®. ®£¤ ª®¥ç ï p-£à㯯 à §à¥è¨¬ .®ª § ⥫ìá⢮.
㦮 ¢®á¯®«ì§®¢ âìáï ¯à¥¤«®¦¥¨¥¬ 1.104 ¨ ⥮६®© 1.72.।«®¦¥¨¥ 1.106.k,ãáâìA, A0 ∈ Mat(t, k),B, B 0 ∈ Mat(t × s, k),C, C 0 ∈ Mat(s, k).®£¤ A0BC 0A0¯à¥¤¥«¥¨¥ 1.107. à㯯 ¢¥àå¥ã¨âà¥ã£®«ìëå«¥¤á⢨¥ 1.108.¬ âà¨æB0C0=AA00AB 0 + BC 0CC 0¢¥àå¥âà¥ã£®«ìëåU T (n, k), k¬ âà¨æT (n, k), k{ ¯®«¥.à㯯 { ¯®«¥. áᬮâਬ ®â®¡à ¦¥¨¥ϕ : T (n, k) → T (n − 1, k) ¯® ¯à ¢¨«ã:¥á«¨X=â®A B0 c∈ T (n, k), £¤¥ A ∈ T (n − 1, k), B ∈ Mat((n − 1) × 1, k), c ∈ k ∗ ,ϕ(X) = A. ®£¤ ϕ ï¥âáï £®¬®¬®à䨧¬®¬ £à㯯, ¯à¨ç¥¬ϕ(U T (n, k)) = U T (n − 1, k).।«®¦¥¨¥ 1.109.T (n, k)0 ⊂ U T (n, k)®ª § ⥫ìá⢮.
®á¯®«ì§®¢ âìáï ¯à¥¤«®¦¥¨¥¬ 1.93.¥®à¥¬ 1.110.à㯯 T (n, k) à §à¥è¨¬ .181. ®ª § ⥫ìá⢮. ® ¯à¥¤«®¦¥¨ï¬ 1.109 ¨ 1.103 ¤®áâ â®ç® ¯®ª § âì, çâ® £à㯯 U T (n, k) à §à¥è¨¬ . 㤥¬ ¢¥á⨠¤®ª § ⥫ìá⢮ ¨¤ãªæ¨¥© ¯® n. ᫨ n = 1,U T (1, k) = 1 ¨ ¯®â®¬ã à §à¥è¨¬ .ãáâì ¤«ï n − 1 ⥮६ ¤®ª § . áᬮâਬ £®¬®¬®à䨧¬ £à㯯â®ϕ : U T (n, k) → U T (n − 1, k)¨§ á«¥¤á⢨ï 1.108. ¬¥â¨¬, çâ®ker ϕ =E0B1∈ U T (n, k),ker ϕN = ker ϕ.® ¯à¥¤«®¦¥¨î 1.106 ¯®«ãç ¥¬, ç⮨¤ãªæ¨¥© ¨ á«¥¤á⢨¥¬ 1.103 ᣤ¥B ∈ Mat((n − 1) × 1, k) .{ ¡¥«¥¢ £à㯯 .áâ ¥âáï ¢®á¯®«ì§®¢ âìáï8. àï¬ë¥ ¯à®¨§¢¥¤¥¨ï £à㯯G ï¥âáï (¢ãâ२¬) ¯àï¬ë¬ ¯à®¨§¢¥¤¥¨¥¬ ᢮¨åG = G1 × · · · × Gn ) ¥á«¨:♥ ª ¦¤ ï ¯®¤£à㯯 Gi ®à¬ «ì ¢ G;♥ ª ¦¤ë© í«¥¬¥â g ∈ G ¨¬¥¥â ¨ ¯à¨â®¬ ¥¤¨á⢥®¥ ¯à¥¤áâ ¢«¥¨¥ ¢ ¢¨¤¥ ¯à®¨§¢¥¤¥¨ï g = g1 · · · gn , £¤¥ gi ∈ Gi . ᫨ G { £à㯯 ®â®á¨â¥«ì® á«®¦¥¨ï, â® £®¢®àïâ, çâ® G ï¥âáï ¯àאַ© á㬬®©á¢®¨å ¯®¤£à㯯 G1 , .
. . , Gn , ¨ ¯¨èãâ G = G1 ⊕ · · · ⊕ Gn .¯à¥¤¥«¥¨¥ 1.111. à㯯믮¤£à㯯G1 , . . . , G n ,(®¡®§ 票¥|G| = |G1 | · · · |Gn |.¯à ¦¥¨¥ 1.112. ®ª § âì, çâ®à¥¤«®¦¥¨¥ 1.113.ãáâìG = G1 × · · · × Gn ¨ gi ∈ Gi , gj ∈ Gj , £¤¥ i 6= j . ®£¤ gi gj = gj gi .«¥¤á⢨¥ 1.114.ãáâìG = G1 ×· · ·×Gn ¨ g = g1 · · · gn , h = h1 · · · hn , £¤¥ gi , hi ∈ Gi¤«ï ¢á¥å i. ®£¤ gh = (g1 h1 ) · · · (gn hn ),g −1 = g1−1 · · · gn−1 .ਬ¥àë 1.115. ¬¥îâáï á«¥¤ãî騥 ¯àï¬ë¥ à §«®¦¥¨ï:C∗ ' U × R∗+ ;Rn = Rk ⊕ Rn−k .(1) £à㯯 (2)।«®¦¥¨¥ 1.116.à㯯 ।«®¦¥¨¥ 1.117.ãáâìZ ¥à §«®¦¨¬ ¢ ¯àï¬ãî á㬬ã.G = G1 × · · · × Gn ¨ g = g1 · · · gn .®£¤ |g| = (|g1 |, . .
. , |gn |).¥®à¥¬ 1.118.ãáâì £à㯯 G = G1 × · · · × Gn ª®¥ç . «¥¤ãî騥 ãá«®¢¨ï íª¢¨-¢ «¥âë:• £à㯯 G 横«¨ç ;• ª ¦¤ ï £à㯯 Gi 横«¨ç ¨ ¯®à浪¨ £à㯯 Gi , i = 1, . . . , n, ¯®¯ à® ¢§ ¨¬®¯à®áâë.®ª § ⥫ìá⢮. ãáâì £à㯯 Gi , i = 1, . . . , n,Gmi = |Gi |.(m1 , m2 ) > 1, â®æ¨ª«¨ç , ¨æ¨ª«¨ç . ᫨, ¯à¨¬¥à,®£¤ ª ¦¤ ï ¯®¤£à㯯 (m1 , .