¤U¤@¶: Zero Divisor ©M Unit
¤W¤@¶: ªì¯Å Ring ªº©Ê½è
«e¤@¶: Ring ªº°ò¥»©w¸q
¦b³o¸`¤¤§Ṳ́¶²Ð¤@¨Çª½±µ¥Î ring ªº©w¸q (¤×¨ä¬O¤À°t²v)
´N¥i±À±oªº°ò¥»©Ê½è.
Y R ¬O¤@Ó ring, ¨ä¥[ªkªº identity §ÚÌ´¿¸g´£¹L²ßºD¤W¬O¥Î 0
¨Óªí¥Ü. ÁöµM³o¤@Ó 0 ¨Ã«D¤j®a¼ô±xªº¨ºÓ 0
¤£¹L´N¦]¬°¥¦©M¤j®a¼ô±xªº 0 ¦³³h¦@³qªº©Ê½è, ©Ò¥H§Ú̥Π0
¨Óªí¥Ü¥¦. þ¨Ç¦@³qªº©Ê½è©O? °£¤F a + 0 = 0 »P
a + x = a x = 0
¥ , ¥H¤Uªº Lemma ¤j®aÀ³¤]«Ü¼ô±x§a!
Lemma 5.2.1
Y
R ¬O¤@Ó ring ¥B 0 ¬O¨ä¥[ªkªº identity, «h¹ï¥ô·Nªº
a R
¬Ò¦³
a . 0 = 0 . a = 0.
µý ©ú.
¤j®aÀ³¥i¥HÆ[¹î¥X 0 ¬O©M¥[ªk¦³Ãöªº, ¦Ó
a . 0 ¤S©M¼ªk¦³Ãö,
©Ò¥H¤£Ãø·Q¹³³oÓ Lemma ¤@©w©M¤À°t²v¦³Ãö.
¥Ñ©ó 0 ¬O¥[ªkªº identity, ¬G¥Ñ (R3) ª¾ 0 + 0 = 0. ¦]¦¹¥Ñ (R8) ±o:
a . 0 = a . (0 + 0) = a . 0 + a . 0.
µM¦Ó¥Ñ (R3) ª¾:
a . 0 + 0 =
a . 0, ¤]´N¬O»¡
x = 0 ©M
x =
a . 0 ¬Ò¬°
a . 0 +
x =
a . 0 ªº¸Ñ. ¬G§Q¥Î Lemma
5.1.2 (2) ¥iª¾
a . 0 = 0.
¦P²z§Q¥Î
(0 + 0) . a = 0 . a ¥i±o
0 . a = 0.
Remark 5.2.2
¦³ªº¦P¾Ç©Î³|§Q¥Î
a . 0 = a . (a - a) = a . a - a . a = 0 |
(5.1) |
³o¤@Óµ¥¦¡¨ÓÃÒ©ú Lemma
5.2.1. ¦¡¤l (
5.1) ¨ä¹ê¬O¦³°ÝÃDªº.
°ÝÃDµo¥Í¦b
R ¤¤¨Ã¨S¦³ ¡u-¡v ³o¤@Ó¹Bºâ. ´«¥y¸Ü»¡¤j®a²ßºD¼gªº
0 =
a -
a À³¸Ó¼g¦¨ 0 =
a + (-
a). ¦]¦¹¦¡¤l (
5.1) À³¸Ó§ï¼g¦¨
a . 0 = a . (a + (- a)) = a . a + a . (- a).
µM¦Ó
a . a +
a . (-
a)
·|µ¥©ó 0 ¶Ü? Y¬O 0 ´Nªí¥Ü
a . (-
a) À³¸Ó¬O
a . a ªº¥[ªk
inverse, ¤]´N¬O
a . (-
a) = - (
a . a).
³o¤@ÂI¨ì¥Ø«e¬°¤î§ÚÌÁÙ¤£ª¾¹D¬O¹ïÁÙ¬O¿ù (¨£ Lemma
5.2.3).
©Ò¥H³o¨Ã¤£¯àÃÒ©ú Lemma
5.2.1.
¨ì©³§Ú̼ô±xªº
a . (- a) = - (a . a) ¹ï¶Ü? ¤U¤@Ó Lemma
§i¶D§Ų́ä¹ê¬O¹ïªº.
Lemma 5.2.3
Y
R ¬O¤@Ó ring, «h¹ï¥ô·Nªº
a,
b R ¬Ò¦³
a . (- b) = (- a) . b = - (a . b).
µý ©ú.
º¥ý¤À²M·¡
a . (-
b) ¬O
a ¼¤W
b ªº¥[ªk inverse, -
a . b
¬O
a ªº¥[ªk inverse ¼¤W
b ¦Ó
- (
a . b) ¬O
a . b ªº¥[ªk
inverse. ©Ò¥HnÃÒ©ú
a . (-
b) = - (
a . b) §ÚÌ¥unÃÒ©ú
(
a . (-
b)) + (
a . b) = 0. µM¦Ó§Q¥Î (R8) ©M Lemma
5.2.1 ª¾
(a . (- b)) + (a . b) = a . ((- b) + b) = a . 0 = 0,
¬G±oÃÒ.
¦P²z¥i±o
(-
a)
. b = - (
a . b).
¦b¤@¯ëªº ring, R ¤¤ - a ¤£¤@©w¥i¥H¼g¦¨
(- 1) . a.
¥Dnªºì¦]¬O 1 ¤£¤@©w¦b R ¤¤, ©Ò¥H -1 ¤£¤@©w¦b R ¤¤.
¦]¦¹¦³¥i¯à¦b R ¤¤
(- 1) . a ¬O¨S¦³·N¸qªº. ¤£¹L¦pªG R ¬O¤@Ó
ring with 1, «h§Q¥Î Lemma 5.2.3 §Ú̽T¹ê¥i±o
(- 1) . a = 1 . (- a) = - a ¥B a . (- 1) = - (a . 1) = - a.
§Q¥Î Lemma 5.2.3 §ÚÌ¥i¥H±o¨ì¥H¤U¤j®a¼ô±xªºµ¥¦¡.
µý ©ú.
¥ý§â -
b ¬Ý¦¨¬O¤@¤¸¯À, ¬G§Q¥Î Lemma
5.2.3 ¥i±o
(-
a)
. (-
b) = - (
a . (-
b)). µM¦Ó¦b®M¥Î¤@¦¸ Lemma
5.2.3 ±o
a . (-
b) = - (
a . b). µ²¦X¥H¤W¤Gµ¥¦¡±o
(- a) . (- b) = - (- (a . b)).
³Ì«á§Q¥Î Lemma
5.1.2 (1) ª¾
- (- (
a . b)) =
a . b, ¬G±oÃÒ
(-
a)
. (-
b) =
a . b.
¥Ñ Lemma 5.2.3 ©M Corollary 5.2.4 §Ú̪¾¹D
¡u-¡v ªº¹Bºâ©M§Ṳ́@¯ë¼ô±xªº¹Bºâ¬Û¦P, ¥H«á§Ú̱N¨Ì²ßºD±N a + (- b)
¼g¦¨ a - b.
¤j®aªì¦¸¬Ý¨ì ring ªº©w¸q®É©Î³|ºÃ´b¥[ªkªºµ²ºc¤¤¬°¦ón¨D¬O¤@Ó
abelian group? ¨Æ¹ê¤W¦pªG·íªì¶Èn¨D¥[ªk¬O¤@Ó group ¦ý¼ªk¦³
identity 1, «h³o·|`±j¢' R ¦b¥[ªk¤§¤U¬O¤@Ó abelian group.
³o¬O¦]¬°¹ï¥ô·Nªº a, b R, ¦Ò¼
(a + b) . (1 + 1)
§ÚÌ·|¦³¥H¤U¨âÓµ¥¦¡:
(a + b) . (1 + 1) = a . (1 + 1) + b . (1 + 1) = (a + a) + (b + b),
(a + b) . (1 + 1) = (a + b) . 1 + (a + b) . 1 = (a + b) + (a + b).
¤]´N¬O»¡
a + a + b + b = a + b + a + b, ¬G¥i±o a + b = b + a.
³Ì«á§ÚÌnª`·Nªº¬O: ·í n ¬O¤@Ó¥¿¾ã¼Æ®É, ¬°¤F¤è«K¤@¯ë§ÚÌ·|²ßºD¥Î
na ¨Óªí¥Ü n Ó a ¬Û¥[©Ò±o¤§È. ¨Ò¦p 2a = a + a, 3a = a + a + a,
...µ¥. ¤£¹L¤d¸U¤£n§â 2a ¼g¦¨ 2 . a, na ¼g¦¨ n . a.
³o¬O¦]¬° 2 ©Î¬O¨ä¥Lªº n ¤£¤@©w·|¦b R ¤¤, ©Ò¥H n ©M a
¬O¤£¯à¬Û¼ªº. ¨º»ò¹ï¥ô·Nªº¥¿¾ã¼Æ n ©M m, §Ṳ́@¯ë¼ô±xªº
(na) . (mb) = (nm)(a . b) ·|¹ï¶Ü? ³o¬O¨S¦³°ÝÃDªº, §A±N na
¼g¦¨ n Ó a ¬Û¥[, mb ¼g¦¨ m Ó b ¬Û¥[, ¦A§Q¥Î¤À°t²v (R8)
¦ÛµM¥iªº nm Ó a . b ¬Û¥[.
¤U¤@¶: Zero Divisor ©M Unit
¤W¤@¶: ªì¯Å Ring ªº©Ê½è
«e¤@¶: Ring ªº°ò¥»©w¸q
Administrator
2005-06-18