¤U¤@¶: Subring
¤W¤@¶: ªì¯Å Ring ªº©Ê½è
«e¤@¶: ¥Ñ Ring ªº©w¸q©Ò±oªº©Ê½è
§Ṳ́w¸gª¾¹D¤@Ó ring ¤¤ªº¥ô·N¤¸¯À¼¤W 0 µ¥©ó 0, ¤£¹L¦b¤@¯ëªº
ring ¤¤¦³¥i¯à¦s¦b¨âÓ¤£µ¥©ó 0 ªº¤¸¯À¬Û¼¥H«áµ¥©ó 0. ¥t¥ ¦b¤@¯ëªº
ring ¤¤¦³¥i¯à¦³¨Ç¤¸¯À¨S¦³¼ªkªº inverse, ©Ò¥H¦³¼ªk inverse
ªº¤¸¯À´NÅã±o«Ü¯S§O¤F. ¦b³o¤@¸`¤¤§Ú̱N°Q½×³o¨âºØ¯S§Oªº¤¸¯À.
Definition 5.3.1
¥O
R ¬O¤@Ó ring. ¦pªG
a 0 ¬O
R ¤¤¤@Ó¤¸¯À¥B¦b
R ¤¤¦s¦b
b 0 ¨Ï±o
a . b = 0 ©Î
b . a = 0, «hºÙ
a ¬O
R ªº¤@Ó
zero-divisor.
·íµM¤F¦b©w¸q¸Ìªº b ¤]¬O R ªº zero-divisor.
Example 5.3.2
¬Û«H¤j®a³£«Ü¤F¸Ñ
³o¤@Ó abelian group.
+
ªº¨úȬO¨ú
a +
b °£¥H 6
ªº¾l¼Æ. ¨Ò¦p
+
=
. ¬Û¦Pªº§Ṳ́]¥i¥H¦b
/6
¤¤©w¤@Ó¼ªk.
. ªºÈ´N¬O
a . b °£¥H 6
ªº¾l¼Æ. ¨Ò¦p
. =
.
¤j®a«Ü®e©öÀˬd¦b³o¼Ëªº¥[ªk©M¼ªk¤§¤U
/6
¬O¤@Ó ring. ¨ä¤¤
¬O
/6
ªº 0 (¥[ªkªº identity). ¦]¬°
¥B
, ¦ý
. =
. ¬G¥Ñ©w¸qª¾
©M
¬O
/6
ªº zero-divisor. ¤S¦]
. =
, ©Ò¥H
¤]¬O zero-divisor. ¥t¥ §ÚÌ¥i¥HÀˬd
©M
¼¤W¤£µ¥©ó
ªº¤¸¯À³£¤£·|µ¥©ó
, ©Ò¥H§Ú̪¾
©M
³£¤£¬O
/6
ªº zero-divisor.
·í a ¬O¤@Ó zero-divisor ®É, «Ü¤£¦nªº¨Æ·|µo¥Í: ´N¬O«Ü¥i¯à
a . x = a . y ¦ý¬O xy (©Î¬O
x . a = y . a ¦ý¬O xy).
¨Ò¦p¦b
/6 ¤¤§Ṳ́£Ãøµo²
. = . = . ·|¾ÉP³o¼Ëªº¬Oµo¥Í¬O¦]¬°Y a ¬O
zero-divisor, °²³] b 0 º¡¨¬
a . b = 0 (©Î
b . a = 0). «h
a . (b + c) = a . b + a . c = 0 + a . c = a . c
(©Î
(b + c) . a = b . a + c . a = 0 + c . a = c . a),
¦ý¬O¥Ñ©ó
b 0, ¬G b + cc.
·í a ¤£¬O zero-divisor ®É, ¤W±©Ò»¡ªº¤£¦n±¡ªp´N¤£·|µo¥Í.
Lemma 5.3.3
·í
a R ¤£¬O ring
R ¤¤ªº zero-divisor ®É, Y
a . b =
a . c ©Î
b . a =
c . a, «h
b =
c.
µý ©ú.
°²¦p
a . b =
a . c, §Y
a . b -
a . c = 0. ¥Ñ Lemma
5.2.3 ª¾
- (
a . c) =
a . (-
c) ¬G
0 = a . b - a . c = a . b + a . (- c) = a . (b - c).
µM¦Ó
a ¤£¬O zero-divisor,
¦]¦¹Y
b -
c 0, «h
a . (
b -
c)
0. ¬G¥Ñ¦¹ª¾
b -
c = 0, ¤]´N¬O»¡
b =
c. ¦P²z¥iÃÒY
b . a =
c . a, «h
b =
c.
Á`¤§, ·í§A¦b³B²z ring ªº°ÝÃD®Éµo² a 0 ¥B
a . b = a . c
§A¤£¥i¥H°¨¤W¤Uµ²½×»¡ b = c, °£«D§Aª¾¹D³oÓ ring ¤¤¨S¦³ zero-divisor.
©Ò¥H¤@Ó¨S¦³ zero-divisor ªº ring ȱo¯S§Oµ¹¥¦¤@Ó¦W¤l.
Definition 5.3.4
¦pªG R ¬O¤@Ó ring ¥B R ¤¤¨S¦³ zero-divisor, «hºÙ R ¬O¤@Ó
domain. ¦pªG R ¬O¤@Ó commutative ring with 1 ¥B¬O¤@Ó
domain, «hºÙ¤§¬°¤@Ó integral domain.
¾ã¼Æ
©Ò§Î¦¨ªº ring ´N¬O³Ì¨å«¬ªº integral domain.
Y R ¬O¤@Ó ring with 1, «h R ¤¤¦³¥i¯à¦s¦b¤¸¯À¥¦ªº¼ªk inverse
¤]¦b R ¤¤. ³o¼Ëªº¤¸¯À¤]¦³«Ü¯S§Oªº©Ê½è.
Definition 5.3.5
Y
R ¬O¤@Ó ring with 1, ¦pªG
a R ¥B¦s¦b
b R ¨Ï±o
a . b =
b . a = 1, «hºÙ
a ¬O
R ªº¤@Ó
unit.
·íµM¤F¦b©w¸q¸Ìªº b ¤]¬O R ªº unit. §Q¥Î Proposition 1.2.2
¤@¼ËªºÃÒ©ú§ÚÌ¥i¥H±o¨ì³oÓ b ¦b R ¤¤¬O°ß¤@ªº. ©Ò¥H·í a ¬O¤@Ó
unit ®É§Ú̳q±`·|¥Î a-1 ªí¥Ü¨ä¼ªkªº inverse.
Example 5.3.6
¦b
/6
³oÓ ring ¤¤
¬O
/6
ªº 1 (¼ªkªº
identity). ¦]
. =
, ¬G
©M
¬O
unit. ¨ä¥Lªº¤¸¯À
,
,
,
³£¤£¬O unit.
Unit ¦³¥H¤U«Ü¦nªº©Ê½è:
Lemma 5.3.7
Y
R ¬O¤@Ó ring with 1 ¥B
a R ¬O¤@Ó unit, «h
- a µ´¹ï¤£·|¬O 0, ¤]¤£·|¬O R ¤¤ªº¤@Ó zero-divisor.
- ¹ï¥ô·Nªº b R, ¤èµ¦¡
a . x = b ©M
y . a = b ¦b R
¤¤³£·|¦³°ß¤@ªº¸Ñ.
µý ©ú.
(1) Y
a = 0, «h¥Ñ Lemma
5.2.1 ª¾
a ¼¤W
R
¤¤¥ô¦óªº¤¸¯À³£µ¥©ó 0, ¬G¤£¥i¯à§ä¨ì¤@¤¸¯À
b ¨Ï±o
a . b = 1.
¦¹©M
a ¬O unit ¥Ù¬Þ, ©Ò¥H
a 0.
¦pªG a ¬O¤@Ó zero divisor, ªí¥Ü¦s¦b c 0 ¨Ï±o
a . c = 0 ©Î
c . a = 0. °²³]¬O
a . c = 0, ¥Ñ°²³] a ¬O unit ª¾
a-1 R, ¬G±o
0 = a-1 . (a . c) = c.
¦¹©M
c 0 ¥Ù¬Þ, ¬Gª¾
a
¤£¬O zero-divisor. ¦P²z¥iÃÒ
c . a = 0 ªº±¡ªp.
(2) ¹ï¥ô·N b R, ¥Ñ°²³] a ¬O unit ª¾
a-1 R, ¬G¥O
x = a-1 . b R ¥i±o
a . x = a . (a-1 . b) = b.
Y
x' R ¤]º¡¨¬
a . x' =
b, ¤]´N¬O»¡
a . x =
a . x', «h¥Ñ
(1) ª¾
a ¤£¬O zero-divisor ¦A¥[¤W Lemma
5.3.3 ª¾
x =
x'.
¦]¦¹¥iª¾
a . x =
b ¦b
R ¤¤¦s¦b°ß¤@ªº¸Ñ. ¦P²z
y . a =
b ¦b
R ¤¤¤]¦³°ß¤@ªº¸Ñ.
§Ú̱j½Õ¤@¤U, ¤@Ó ring ¤¤ªº unit µ´¹ï¤£¬O zero-divisor,
¤£¹LY¤@Ó¤¸¯À¤£¬O zero-divisor ¨Ã¤£ªí¥Ü¥¦·|¬O unit. ¨Ò¦p¦b
¤¤
2 ¤£¬O zero-divisor, ¦ý¥¦¤]¤£¬O
ªº unit.
¥Ñ Lemma 5.3.7 ª¾¦b R ¤¤ 0 µ´¹ï¤£·|¬O¤@Ó unit. ¦pªG°£¤F
0 ¥H¥ ¨ä¥Lªº¤¸¯À³£¬O unit ³o»ò¯S§Oªº ring
¤]ȱoµ¹¥¦¤@Ó¯S§Oªº¦W¤l.
Definition 5.3.8
Y R ¬O¤@Ó ring with 1 ¥B R ¤¤«D 0 ªº¤¸¯À³£¬O unit, «hºÙ
R ¬O¤@Ó division ring. Y R ¬O¤@Ó commutative ring
¥B¬O¤@Ó division ring, «hºÙ R ¬O¤@Ó field.
¦³²z¼Æ
©Ò¦¨ªº ring ´N¬O¤@Ө嫬ªº field.
³Ì«á§ÚÌn±j½Õ: ¦pªG R ¬O¤@Ó division ring, «h¥Ñ©ó R ¤¤ªº«D 0
¤¸¯À³£¬O unit ©Ò¥H³£¤£¬O zero-divisor. ¦]¦¹¨âÓ«D 0
¤¸¯À¬Û¼³£¤£µ¥©ó 0. ¤]´N¬O R ¤¤«D 0
ªº¤¸¯À©Ò¦¨ªº¶°¦X¦b¼ªk¤§¤U¬O«Ê³¬ªº. ¦A¥[¤W³o¨Ç¤¸¯À³£¦³¼ªkªº
inverse, ©Ò¥H R ¤¤«D 0 ªº¤¸¯À©Ò¦¨ªº¶°¦X¦b¼ªk¤§¤U¬O¤@Ó group.
¤×¨ä·í R ¬O¤@Ó field ®É, R ¤¤«D 0
ªº¤¸¯À©Ò¦¨ªº¶°¦X¦b¼ªk¤§¤U¬O¤@Ó abelian group.
¤U¤@¶: Subring
¤W¤@¶: ªì¯Å Ring ªº©Ê½è
«e¤@¶: ¥Ñ Ring ªº©w¸q©Ò±oªº©Ê½è
Administrator
2005-06-18