¤U¤@¶: Unique Factorization Domain
¤W¤@¶: Integral Domain ¤Wªº¤À¸Ñ©Ê½è
«e¤@¶: Euclidean Domain
³o¤@¸`¤¤§Ú̱N±´°Q principle ideal domain ªº°ò¥»©Ê½è. ¥Ñ©ó¤wª¾¤@Ó
Euclidean domain ¤@©w¬O principle ideal domain,
©Ò¥H³o¤@¸`©Ò½Íªº©Ê½è·íµM¾A¥Î©ó Euclidean Domain.
«e±´£¹L¹ï¤@¯ëªº integral domain ¥ôµ¹¨âÓ«D 0 ¤¸¯À¨ä greatest
common divisor ¤£¤@©w¦s¦b. ¤£¹L¹ï©ó principle ideal domain,
¥ô·N¨âÓ«D 0 ¤¸¯À¤§ greatest common divisor ´N¤@©w¦s¦b¤F!
Proposition 8.3.1
°²³]
R ¬O¤@Ó principle ideal domain. ¹ï¥ô·N
a,
b R ¥B
a,
b 0 ¨ä greatest common divisor ¦s¦b. ¦Ó¥B, Y
d ¬O
a,
b ªº¤@Ó
greatest common divisor, «h¦s¦b
r,
s R ¨Ï±o
d =
r . a +
s . b.
µý ©ú.
º¥ý¦Ò¼
a +
b ³o¤@Ó ideal. ¥Ñ©ó
R ¬O principle ideal
domain, ¬G¦s¦b
d R º¡¨¬
d =
a +
b. §ÚÌ·QnÃÒ©ú
d ´N¬O
a,
b ªº greatest common divisor.
º¥ý¥ýÃÒ©ú d ¬O a, b ªº common divisor. ¥Ñ©ó
¬G¥Ñ Lemma
8.1.2 ª¾
d |
a. ¦P²z¥iÃÒ
d |
b, ¬G±o
d ¬O
a,
b
ªº¤@Ó common divisor.
±µ¤U¨ÓÃÒ©úY c ¬O a, b ªº¤@Ó common divisor, «h c | d.
µM¦ÓY c | a ¥B c | b, ªí¥Ü
a c ¥B
b c. ¥Ñ©ó
c ¬O¤@Ó ideal,
¥¦¦³¥[ªkªº«Ê³¬©Ê, ¬G±o
a + b c. ¤]´N¬O»¡
d c. ¬G±oÃÒ c | d.
³Ì«á¥Ñ©w¸q,
a + b ¤¤ªº¤¸¯À³£¬O
r . a + s . b, ¨ä¤¤
r, s R ³oºØ§Î¦¡. ¬G¥Ñ
d d = a + b ª¾¤@©w¦s¦b
r, s R ¨Ï±o
d = r . a + s . b. ³oÓ¯S©Ê¹ï©ó¥ô·N a, b ªº
greatest common divisor ¬Ò¹ï. ³o¬O¦]¬°¥Ñ Lemma 8.1.6 ª¾Y
d' ¬O a, b ¥t¤@Ó greatest common divisor, «h§Ų̵́M¦³
d' = d = a + b.
``Y d ¬O a, b ªº¤@Ó greatest common divisor, «h¦s¦b r, s R
º¡¨¬
d = r . a + s . r'' ³o¤@Ó¯S©Ê«D±`¦³¥Î.
¤j®a¥i¥H§Q¥Î³oÓ¯S©Ê¦A¥é·Ó Proposition 7.1.7 ©Î Proposition
7.2.11 ªºµý©ú¤è¦¡ÃÒ±o¤@Ó principle ideal domain ¤¤ªº
irreducible element ³£¬O prime element. ¤£¹L³o¸Ì§Ṳ́¶²Ð¥t¤@ºØ§Q¥Î
ideal ¤èªkªºÃÒ©ú.
Lemma 8.3.2
°²³]
R ¬O¤@Ó principle ideal domain,
a R ¥B
a 0. Y
a
¬O
R ªº¤@Ó irreducible element «h
a ¬O
R ªº¤@Ó maximal
ideal. ¤Ï¤§, Y
a ¬O
R ªº¤@Ó maximal ideal, «h
a ¬O
R
ªº¤@Ó irreducible element.
µý ©ú.
¦pªG
a ¬O¤@Ó irreducible element, ¥Ñ Lemma
8.1.9 (1)
§Ú̪¾¹D§ä¤£¨ì¤@Ó nontrivial ªº principle ideal ¤¶©ó
a ©M
R ¤§¶¡. ¤£¹L¥Ñ
R ¬O principle ideal ªº°²³]ª¾
R ¤¤ªº ideal ³£¬O
principle ideal. ´«¥y¸Ü»¡´N¬O§ä¤£¨ì¤@Ó ideal ¤¶©ó
a ©M
R
¤§¶¡. ¬G±o
a ¬O¤@Ó maximal ideal.
¤Ï¤§, ¦pªG
a ¬O¤@Ó maximal ideal, ·íµM§ä¤£¨ì nontrivial
principle ideal ¥]§t
a. ¬G§Q¥Î Lemma 8.1.9 (1) ª¾
a ¬O¤@Ó irreducible element.
¦^ÅU¤@¤U Lemma 8.1.9 ªº¥t¤@³¡¤À¬O»¡ a ¬O prime element
Y¥B°ßY
a ¬O¤@Ó prime ideal.
©Ò¥H§Ú̫ܧ֪º´N¥i¥H±o¨ì¥H¤U¤§µ²ªG.
Proposition 8.3.3
°²³]
R ¬O¤@Ó principle ideal domain, «h
R ¤¤ªº irreducible
element ³£¬O prime element. ¤Ï¤§,
R ¤¤ªº prime element ³£¬O
irreducible element.
µý ©ú.
¦]¬°
R ¬O integral domain, Lemma
8.1.8 §i¶D§ÚÌ
R ¤¤ªº
prime element ³£¬O irreducible element.
¤Ï¤§, Y a ¬O R ¤¤ªº irreducible element, ¥Ñ Lemma 8.3.2
ª¾
a ¬O R ªº¤@Ó maximal ideal. µM¦Ó Corollary 6.5.13
§i¶D§ÚÌ R ¤¤ªº maximal ideal ³£¬O prime ideal, ¬Gª¾
a ¬O
R ªº¤@Ó prime ideal. ¦]¦¹§Q¥Î Lemma 8.1.9 (2) ±oÃÒ a
¬O¤@Ó prime element.
«e±´£¹L¦b¤@¯ëªº commutative ring with 1 ¤¤ªº maximal ideal ³£¬O
prime ideal, ¦ý¬O prime ideal ¥¼¥²¬O maximal ideal. µM¦Ó Lemma
8.3.2 ¥H¤Î Proposition 8.3.3 ±N principle ideal
domain ¤¤ªº maximal ideal ©M prime ideal µ¹¤F¤@Ó«nªºÃö³s.
Corollary 8.3.4
°²³]
R ¬O¤@Ó principle ideal domain ¥B
I ¬O
R ¤¤¤@Ó«D 0 ªº
ideal. «h
I ¬O¤@Ó prime ideal Y¥B°ßY
I ¬O¤@Ó maximal ideal.
§ÚÌ´¿¸g§Q¥Î
©M F[x] ¤¤ªº irreducible element ©M prime
element ¬O¬Û¦PªºÃÒ©ú
©M F[x] ªº°ß¤@¤À¸Ñ©Ê½è.
§Ú̲¦b´X¥G¤w¨ì¹F¥i¥HÃÒ©ú principle ideal domain
ªº°ß¤@¤À¸Ñ©Ê½èªº¥Ø¼Ð. ¤£¹L·í®É§Ú̦b
©M F[x]
¤¤¬O§Q¥Î¼Æ¾ÇÂk¯Çªk¨ÓÃÒ©ú°ß¤@¤À¸Ñ©Ê½è, ²¦b¦b¤@¯ëªº principle ideal
domain §Ų́S¿ìªk¨Ï¥Î¼Æ¾ÇÂk¯Çªk. ¤U¤@Ó Lemma
¥i¥HÀ°§U§Ú̧JªA³oÓ§xÃø.
Lemma 8.3.5
°²³]
R ¬O¤@Ó principle ideal domain, «hµLªk¦b
R
¤¤§ä¨ìµL½a¦hÓÄY®æ»¼¼Wªº ideals. ´«¥y¸Ü»¡¦pªG
{
In}
n = 1
¬O¤@²Õ
R ¤¤ªº ideal º¡¨¬
«h¦s¦b
m ¨Ï±o
Im =
Im + 1 =
... .
µý ©ú.
º¥ý§Ú̦Ҽ
I =
In ³o¤@Ó¶°¦X. §ÚÌ·QnÃÒ©ú
I
¬O
R ¤¤ªº ideal. (nª`·N¤@¯ë¨ÓÁ¿Y
J1,
J2 ¬O
R ªº ideal ¨º»ò
J1 J2 ¤£¤@©w¬O
R ªº ideals. ¤£¹L¦b³o¸Ì¥Ñ©ó
In
¦³¥]§tªºÃö«Y, §ÚÌ¥i¥HÃÒ¥X
I ¬O¤@Ó ideal.)
°²³] a, b I, ´«¥y¸Ü»¡¦s¦b
i, j ¨Ï±o a Ii ¥B b Ij. °²³] ij, ¥Ñ°²³]ª¾
Ij Ii. ¬G±o
a, b Ii.
¦]¦¹¥Ñ Ii ¬O¤@Ó ideal, §Ú̦³
a - b Ii. ©Ò¥H±o a - b I.
¥t¥ Y a I ¥B r R, ¥Ñ°²³]ª¾¦s¦b
i ¨Ï±o a Ii.
¬G±o
a . r Ii, ¤]´N¬O»¡
a . r I. ¬G¥Ñ Lemma
6.1.2 ª¾ I ¬O R ¤¤ªº¤@Ó ideal.
¬JµM I ¬O R ªº ideal ¥B R ¬O principle ideal domain, ¬G¦s¦b
a R ¨Ï±o
a = I. µM¦Ó§Q¥Î
a a = I ª¾¦s¦b
m ¨Ï±o a Im. ¬G§Q¥Î
a ¬O¥]§t a ³Ì¤pªº ideal
(Lemma 6.5.1) ª¾
I = a Im. ´«¥y¸Ü»¡ I = Im,
¦]¦¹§Q¥Î¹ï©Ò¦³ªº i > m ¬Ò¦³
Im Ii ¥H¤Î
Ii I
±oÃÒ I = Im = Ii,
i > m.
§ÚÌnÂǥΠLemma 8.3.5 ªº¥Dnì¦]¬O¦pªG d ¬O a ªº¤@Ó
nontrivial divisor (§Y d | a ¦ý d ¤£¬O unit ¥B©M a ¤£
associates), «h
a d. ¦p¦¹¤@¨Ó, ¥i¥HÃÒ¥X R
¤¤ªº¤¸¯À¥u¯à¼g¦¨¦³¦hÓ irreducible element ªº¼¿n.
Theorem 8.3.6
°²³]
R ¬O¤@Ó principle ideal domain ¥B
a ¬O
R ¤¤¤£¬° 0
¥B¤£¬O unit ªº¤¸¯À, «h
a ¥i¥H¼g¦¨¦³¦hÓ
R ¤¤ªº irreducible
elements ªº¼¿n, ¦Ó¥BY©¿²¤ associates ªºÃö«Y¥H¤Î¼ªkªº¶¶§Ç,
³oÓ¼¿nªº¼gªk°ß¤@. ¤]´N¬O»¡¦pªG
a |
= |
p1n1 ... prnr |
|
|
= |
q1m1 ... qsms |
|
¨ä¤¤
p1,...,
pr ¬O¨â¨â¤£¬Û associates ªº
irreducible elements ¥B
q1,...,
qs ¬O¨â¨â¤£¬Û associates ªº
irreducible elements, «h¸g¹L¾A·íªºÅÜ´«¶¶§Ç, §Ú̦³
r =
s,
pi qi ¥H¤Î
ni =
mi,
i = 1,...,
r.
µý ©ú.
º¥ý§ÚÌÃÒ©ú
a ¥i¥H¼g¦¨¦³¦hÓ irreducible elements ªº¼¿n. ¦pªG
a ¤£¯à¼g¦¨¦³¦hÓ irreducible elements ªº¼¿n, ªí¥Ü
a ¥»¨¤£¬O
irreducible, ¦]¦¹
a =
a1 . b1, ¨ä¤¤
a1,
b1 R ¬O
a ªº
nontrivial divisors ¥B
a1,
b1 ¤¤¥²¦³¤@Ó¤£¯à¼g¦¨¦³¦hÓ
irreducible elements ªº¼¿n. °²³]¬O
a1, ¦P¤W§Ú̪¾¦s¦b
a2,
b2 R ¨Ï±o
a1 =
a2 . b2, ¨ä¤¤
a2 ¬O
a1 ªº
nontrivial divisor ¥B
a2 ¤£¯à¼g¦¨¦³¦hÓ irreducible elements
ªº¼¿n. ¦p¦¹¤@ª½¤U¥h§ÚÌ»s³y¤F¤@³s¦êªº ideals ²Å¦X
¦¹©M Lemma
8.3.5 ¥Ù¬Þ, ¬Gª¾
a ¤@©w¥i¥H¼g¦¨¦³¦hÓ
irreducible elements ªº¼¿n.
±µ¤U¨Ó§ÚÌÃҰߤ@©Ê. ¤@¯ë¨Ó»¡Y¤wÃÒ±o irreducible element ´N¬O prime
element °ß¤@©Ê´N¦Û°Ê¦¨¥ß. ³o¬O¦]¬°¦pªG
a = p1n1 ... prnr = q1m1 ... qsms,
¥ô¨ú
pi ¥Ñ©ó
pi | q1m1 ... qsms,
¥B
pi ¬O prime (Proposition
8.3.3) ª¾¦s¦b
j {1,...,
s} ¨Ï±o
pi |
qj. ´«¨¥¤§
pi ¬O
qj ªº¤@Ó divisor. µM¦Ó
qj ¬O irreducible ¥B
pi
¤£¬O unit, ¬G±o
pi qj (§Y
pi ©M
qj associates).
¦]¦¹§Ú̪¾¹D¹ï³oÓ
pi, ¦b
{
q1,...,
qs} ¤¤¥u¯à§ä¨ì°ß¤@ªº
qj ¨Ï±o
pi qj. §_«hY
jj' ¦ý
pi |
qj', «h
¦P²z¥i±o
pi qj', §Q¥Î associates ¬OÓ equivalence relation
§Ú̱o
qj qj', ³o©M°²³]Y
jj' «h¤£¥i¯à
qj qj' ¬Û¥Ù¬Þ. ¤Ï¤§¹ï¥ô·Nªº
qj §ÚÌ¥i¥H¦b
{
p1,...,
pr} ¤¤§ä¨ì°ß¤@ªº
pi ¨Ï±o
qj pi.
¦]¦¹§Ú̦b
{
p1,...,
pr} ©M
{
q1,...,
qs}
³o¨âÓ¶°¦X¤¤§ä¨ì¤@¹ï¤@ªº¹ïÀ³. ¤]´N¬O»¡
r =
s ¥B¸g¹L¾A·íªº«±Æ§Ú̦³
p1 q1,...,
pr qr. ²°²³]¬YÓ
nimi,
¬°¤F¤è«K°_¨£§ÚÌ´N°²³]
n1m1 ¥B
n1 >
m1 §a! ¥Ñ©ó
q1 =
u . p1, ¨ä¤¤
u ¬O
R ªº¤@Ó unit, §Ú̦³
p1m1(p1n1 - m1 . p2n2 ... prnr - um1 . q2m2 ... qrmr) = 0.
§Q¥Î
p1m1 0 ¥B
R ¬O integral domain, §Ú̦³
p1n1 - m1 . p2n2 ... prnr = um1 . q2m2 ... qrmr.
µM¦Ó¥Ñ©ó
n1 -
m1 > 0, ¥i±o¦b
{
q2,...,
qr} ¤¤¦s¦b
qj ¨Ï±o
p1 |
qj (ª`·N
u ¬O
unit ¬G¤£¥i¯à
p1 |
u). ¤]´N¬O»¡
p1 qj, ¦ý³o©M
q1 ¬O
{
q1,...,
qr} ¤¤°ß¤@º¡¨¬©M
p1 associates ªº¤¸¯À¬Û¥Ù¬Þ.
±oÃÒ¥»©w²z.
º¡¨¬ Theorem 8.3.6 ¤¤ªº°ß¤@¤À¸Ñ©Ê½èªº ring «D±`«n,
§Ṳ́]µ¹¥¦¤@Ó¯S®íªº¦W¤l.
Definition 8.3.7
°²³] R ¬O¤@Ó integral domain ¦Ó¥B R ¤¤«D 0 ¥B¤£¬O unit
ªº¤¸¯À³£¥i¥H¼g¦¨¦³¦hÓ R ¤¤ªº irreducible elements ªº¼¿n,
¦Ó¥BY©¿²¤ associates ªºÃö«Y¥H¤Î¼ªkªº¶¶§Ç, ³oÓ¼¿nªº¼gªk°ß¤@, «hºÙ
R ¬O¤@Ó unique factorization domain.
Theorem 8.3.6 §i¶D§Ṳ́@Ó principle ideal domain
¤@©w¬O¤@Ó unique factorization domain. ¦ý¬O¤@Ó unique
factorization domain ¨Ã¤£¤@©w¬O principle ideal domain. §ÚÌ´¿¸g¨£¹L
[x] ¬O¤@Ó unique factorization domain (Theorem 7.3.13)
¦ý¨ä¤¤
2 + x ³o¤@Ó ideal ¨Ã¤£¬O principle ideal
(Example 7.3.1).
¤U¤@¶: Unique Factorization Domain
¤W¤@¶: Integral Domain ¤Wªº¤À¸Ñ©Ê½è
«e¤@¶: Euclidean Domain
Administrator
2005-06-18