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¤U¤@­¶: Subring ¤W¤@­¶: ªì¯Å Ring ªº©Ê½è «e¤@­¶: ¥Ñ Ring ªº©w¸q©Ò±oªº©Ê½è

Zero Divisor ©M Unit

§Ú­Ì¤w¸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¤@¸`¤¤§Ú­Ì±N°Q½×³o¨âºØ¯S§Oªº¤¸¯À.

Definition 5.3.1   ¥O R ¬O¤@­Ó ring. ¦pªG a$ \ne$ 0 ¬O R ¤¤¤@­Ó¤¸¯À¥B¦b R ¤¤¦s¦b b$ \ne$ 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

$\displaystyle \mathbb {Z}$/6$\displaystyle \mathbb {Z}$ = {$\displaystyle \overline{0}$,$\displaystyle \overline{1}$,$\displaystyle \overline{2}$,$\displaystyle \overline{3}$,$\displaystyle \overline{4}$,$\displaystyle \overline{5}$}

³o¤@­Ó abelian group. $ \overline{a}$ + $ \overline{b}$ ªº¨ú­È¬O¨ú a + b °£¥H 6 ªº¾l¼Æ. ¨Ò¦p $ \overline{2}$ + $ \overline{5}$ = $ \overline{1}$. ¬Û¦Pªº§Ú­Ì¤]¥i¥H¦b $ \mathbb {Z}$/6$ \mathbb {Z}$ ¤¤©w¤@­Ó­¼ªk. $ \overline{a}$ . $ \overline{b}$ ªº­È´N¬O a . b °£¥H 6 ªº¾l¼Æ. ¨Ò¦p $ \overline{2}$ . $ \overline{5}$ = $ \overline{4}$. ¤j®a«Ü®e©öÀˬd¦b³o¼Ëªº¥[ªk©M­¼ªk¤§¤U $ \mathbb {Z}$/6$ \mathbb {Z}$ ¬O¤@­Ó ring. ¨ä¤¤ $ \overline{0}$ ¬O $ \mathbb {Z}$/6$ \mathbb {Z}$ ªº 0 (¥[ªkªº identity). ¦]¬° $ \overline{2}$$ \ne$$ \overline{0}$ ¥B $ \overline{3}$$ \ne$$ \overline{0}$, ¦ý $ \overline{2}$ . $ \overline{3}$ = $ \overline{0}$. ¬G¥Ñ©w¸qª¾ $ \overline{2}$ ©M $ \overline{3}$ ¬O $ \mathbb {Z}$/6$ \mathbb {Z}$ ªº zero-divisor. ¤S¦] $ \overline{4}$ . $ \overline{3}$ = $ \overline{0}$, ©Ò¥H $ \overline{4}$ ¤]¬O zero-divisor. ¥t¥ §Ú­Ì¥i¥HÀˬd $ \overline{1}$ ©M $ \overline{5}$ ­¼¤W¤£µ¥©ó $ \overline{0}$ ªº¤¸¯À³£¤£·|µ¥©ó $ \overline{0}$, ©Ò¥H§Ú­Ìª¾ $ \overline{1}$ ©M $ \overline{5}$ ³£¤£¬O $ \mathbb {Z}$/6$ \mathbb {Z}$ 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 x$ \ne$y (©Î¬O x . a = y . a ¦ý¬O x$ \ne$y). ¨Ò¦p¦b $ \mathbb {Z}$/6$ \mathbb {Z}$ ¤¤§Ú­Ì¤£Ãøµo² $ \overline{2}$ . $ \overline{1}$ = $ \overline{2}$ . $ \overline{4}$ = $ \overline{2}$. ·|¾É­P³o¼Ëªº¬Oµo¥Í¬O¦]¬°­Y a ¬O zero-divisor, °²³] b$ \ne$ 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$ \ne$ 0, ¬G b + c$ \ne$c.

·í a ¤£¬O zero-divisor ®É, ¤W­±©Ò»¡ªº¤£¦n±¡ªp´N¤£·|µo¥Í.

Lemma 5.3.3   ·í a $ \in$ 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$ \ne$ 0, «h a . (b - c)$ \ne$ 0. ¬G¥Ñ¦¹ª¾ b - c = 0, ¤]´N¬O»¡ b = c. ¦P²z¥iÃÒ­Y b . a = c . a, «h b = c. $ \qedsymbol$

Á`¤§, ·í§A¦b³B²z ring ªº°ÝÃD®Éµo² a$ \ne$ 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 ­È±o¯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 $ \mathbb {Z}$ ©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 $ \in$ R ¥B¦s¦b b $ \in$ 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§Ú­Ì³q±`·|¥Î a-1 ªí¥Ü¨ä­¼ªkªº inverse.

Example 5.3.6   ¦b $ \mathbb {Z}$/6$ \mathbb {Z}$ ³o­Ó ring ¤¤ $ \overline{1}$ ¬O $ \mathbb {Z}$/6$ \mathbb {Z}$ ªº 1 (­¼ªkªº identity). ¦] $ \overline{5}$ . $ \overline{5}$ = $ \overline{1}$, ¬G $ \overline{1}$ ©M $ \overline{5}$ ¬O unit. ¨ä¥Lªº¤¸¯À $ \overline{0}$,$ \overline{2}$,$ \overline{3}$,$ \overline{4}$ ³£¤£¬O unit.

Unit ¦³¥H¤U«Ü¦nªº©Ê½è:

Lemma 5.3.7   ­Y R ¬O¤@­Ó ring with 1 ¥B a $ \in$ R ¬O¤@­Ó unit, «h

  1. a µ´¹ï¤£·|¬O 0, ¤]¤£·|¬O R ¤¤ªº¤@­Ó zero-divisor.

  2. ¹ï¥ô·Nªº b $ \in$ 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$ \ne$ 0.

¦pªG a ¬O¤@­Ó zero divisor, ªí¥Ü¦s¦b c$ \ne$ 0 ¨Ï±o a . c = 0 ©Î c . a = 0. °²³]¬O a . c = 0, ¥Ñ°²³] a ¬O unit ª¾ a-1 $ \in$ R, ¬G±o

0 = a-1 . (a . c) = c.

¦¹©M c$ \ne$ 0 ¥Ù¬Þ, ¬Gª¾ a ¤£¬O zero-divisor. ¦P²z¥iÃÒ c . a = 0 ªº±¡ªp.

(2) ¹ï¥ô·N b $ \in$ R, ¥Ñ°²³] a ¬O unit ª¾ a-1 $ \in$ R, ¬G¥O x = a-1 . b $ \in$ R ¥i±o

a . x = a . (a-1 . b) = b.

­Y x' $ \in$ 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. $ \qedsymbol$

§Ú­Ì±j½Õ¤@¤U, ¤@­Ó ring ¤¤ªº unit µ´¹ï¤£¬O zero-divisor, ¤£¹L­Y¤@­Ó¤¸¯À¤£¬O zero-divisor ¨Ã¤£ªí¥Ü¥¦·|¬O unit. ¨Ò¦p¦b $ \mathbb {Z}$ ¤¤ 2 ¤£¬O zero-divisor, ¦ý¥¦¤]¤£¬O $ \mathbb {Z}$ 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 ¤]­È±oµ¹¥¦¤@­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 $ \mathbb {Q}$ ©Ò¦¨ªº ring ´N¬O¤@­Ó¨å«¬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.


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