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¤U¤@­¶: ¤@¨Ç±`¨£ªº Rings ¤W¤@­¶: ¯S®íªº Ideals «e¤@­¶: Prime ideals

Maximal ideals

¦b $ \mathbb {Z}$ ¤¤½è¼Æ¥t¤@­Ó­«­nªº©Ê½è¬O°£¤F 1 ©M¥»¨­¥ ¥¦¤£·|¬O¨ä¥L¾ã¼Æªº­¿¼Æ. ¥H«á§Ú­Ì·|ª¾¹D¦b¾ã¼Æ¤¤©Ò¦³ªº ideal ¬Ò¬O principle ideal. ©Ò¥H¥Î ideal ªºÆ[ÂI¨Ó¬Ý³oªí¥Ü¤@­Ó½è¼Æ©Ò§Î¦¨ªº principle ideal ¤£·|¥]§t©ó¨ä¥Lªº nontrivial proper ideal. ¦]¦¹§Ú­Ì¦³¥H¤U¥t¤@­Ó±À¼s½è¼Æ©Ê½èªº¯S®í ideal.

Definition 6.5.9   ­Y R ¬O¤@­Ó ring ¥B M ¬O R ¤¤ªº¤@­Ó nontrivial proper ideal, ¦pªG M ¤£·|¥]§t©ó R ¤¤¨ä¥Lªº nontrivial proper ideal, «h§Ú­ÌºÙ M ¬O¤@­Ó maximal ideal.

ª`·N, §O³Q ``maximal'' ³o­Ó¦rµ¹ÄF¤F. ¦b¼Æ¾Ç¤W«Ü¦h±¡ªp¤U, maximal ¬Oªí¥Ü¨S¦³ªF¦è¤ñ¥¦¤j, ¨Ã¤£ªí¥Ü¥¦¤ñ©Ò¦³ªºªF¦è¤j. (§Ú­Ì¤£³o¼Ë©w¥D­n¬O¦b«Ü¦h±¡ªp¤U§Ú­Ì­n±´°QªºªF¦è¨Ã¤£¬O well-ordered, ¤]´N¬O¦³®É¨â¼ËªF¦è¬O¤£¯à¤ñ¸ûªº.) ¦]¦¹, ­Y M ¬O R ªº¤@­Ó maximal ideal ¥B I ¬O R ªº¤@­Ó nontrivial proper ideal, ³o¨Ã¤£ªí¥Ü I $ \subseteq$ M, ¦Ó¥u¬O»¡¦pªG M $ \subseteq$ I, «h I = M. ±q³o­Ó¬Ýªk¤j®aÀ³¤]¥i¥H¬Ý¥X¦³¥i¯à¦b R ¤¤¦³¤£¥u¤@­Ó maximal ideal. §Æ±æ¤U¤@­Ó¨Ò¤l¥i¥HÂç²M³o­ÓÆ[©À.

Example 6.5.10   ¦Ò¼ $ \mathbb {Z}$ ¤¤ $ \bigl($6$ \bigr)$ ³o¤@­Ó ideal. §Ú­Ì«Ü®e©ö¬Ý¥X¨Ó $ \bigl($6$ \bigr)$ $ \subseteq$ $ \bigl($2$ \bigr)$ ¥B¦] 2 $ \in$ $ \bigl($2$ \bigr)$ ¦ý 2 $ \not\in$$ \bigl($6$ \bigr)$, §Ú­Ìª¾ $ \bigl($6$ \bigr)$ $ \subsetneq$ $ \bigl($2$ \bigr)$. ¦A¥[¤W $ \bigl($2$ \bigr)$ ¬O $ \mathbb {Z}$ ªº¤@­Ó nontrivial proper ideal, ¬Gª¾ $ \bigl($6$ \bigr)$ ¤£¬O $ \mathbb {Z}$ ªº maximal ideal. ¤£¹L $ \bigl($2$ \bigr)$ ¬O $ \mathbb {Z}$ ªº maximal ideal. ¦]¬°¦pªG $ \bigl($2$ \bigr)$ ¤£¬O maximal ideal, «h¨Ì©w¸qª¾¦s¦b¤@­Ó $ \mathbb {Z}$ ¤¤ªº nontrivial proper ideal I º¡¨¬ $ \bigl($2$ \bigr)$ $ \subsetneq$ I. ´«¥y»¡¦s¦b¤@¾ã¼Æ a $ \in$ I ¦ý a $ \not\in$$ \bigl($2$ \bigr)$ (³oªí¥Ü a ¬O¤@­Ó©_¼Æ). ©Ò¥H¦s¦b¤@¾ã¼Æ n ¨Ï±o a = 2 . n + 1. §O§Ñ¤F§Ú­Ì°²³] I ¬O ideal ¥B 2 $ \in$ I, ©Ò¥H 2 . n $ \in$ I. ¦A¥[¤W a $ \in$ I, ¦]¦¹±o 1 = a - 2 . n $ \in$ I. ¥Ñ Lemma 6.2.4 ª¾ I = $ \mathbb {Z}$, ³o©M§Ú­Ì°²³] I ¬O nontrivial proper ideal ¬Û¥Ù¬Þ, ¬G±o $ \bigl($2$ \bigr)$ ¬O $ \mathbb {Z}$ ªº maximal ideal. ¤£¹L¥Ñ©ó 3 $ \not\in$$ \bigl($2$ \bigr)$, §Ú­Ìª¾ $ \bigl($3$ \bigr)$ ³o­Ó ideal ¨Ã¤£¥]§t©ó $ \bigl($2$ \bigr)$. ¬Æ¦Ü¹ï¥ô·Nªº n $ \in$ $ \mathbb {N}$, $ \bigl($3n$ \bigr)$ ³£¤£·|¥]§t©ó $ \bigl($2$ \bigr)$. ©Ò¥H maximal ideal ·|¤ñ©Ò¦³ªº nontrivial proper ideal ³£¤j³o¼Ëªº»¡ªk¨Ã¤£¥¿½T. ¥t¤@¤è­±, §Ú­Ì¥i¥H¥Î«e­±Ãþ¦üªº¤èªk±o¨ì¦b $ \mathbb {Z}$ ¤¤¥ô·N¤@­Ó½è¼Æ©Ò²£¥Íªº principle ideal ³£¬O maximal ideal, ©Ò¥H $ \mathbb {Z}$ ¤¤ªº maximal ideal ¨Ã¤£¥u¤@­Ó (¨ä¹ê¦³µL½a¦h­Ó).

±µ¤U¨Ó§Ú­Ì·Q¥ÎÃþ¦ü Theorem 6.5.7 ªº¤èªk§Q¥Î quotient ring ¨Ó§P§O¤@­Ó ideal ¬O§_¬° maximal ideal.

Theorem 6.5.11   ­Y R ¬O¤@­Ó commutative ring with 1 ¥B M ¬O R ªº¤@­Ó ideal, «h M ¬O R ªº¤@­Ó maximal ideal ­Y¥B°ß­Y R/M ³o­Ó quotient ring ¬O¤@­Ó field.

µý ©ú. ­º¥ýÆ[¹î¥Ñ°²³]¥iª¾ R/M ¬O¤@­Ó commutative ring with 1, ©Ò¥H R/M ¬O¤@­Ó field ¬Û·í©ó¥u­n»¡ R/M ¤¤¤£µ¥©ó $ \overline{0}$ ªº¤¸¯À³£¬O unit.

²°²³] M ¬O R ªº maximal ideal. ¥ô¨ú R/M ¤¤¤@¤¸¯À $ \overline{a}$$ \ne$$ \overline{0}$, §Ú­Ì¦³ a $ \in$ R ¥B a $ \not\in$M. ¥Ñ Lemma 6.2.1 ª¾

M + $\displaystyle \bigl($a$\displaystyle \bigr)$ = {m + r . a | m $\displaystyle \in$ Mr $\displaystyle \in$ R}

¬O R ªº¤@­Ó ideal. ¥Ñ©ó M $ \subseteq$ M + $ \bigl($a$ \bigr)$ ¥B a $ \not\in$M, §Ú­Ìª¾ M$ \ne$M + $ \bigl($a$ \bigr)$, §Y M + $ \bigl($a$ \bigr)$ ¬O¤@­Ó¤ñ M ¤jªº ideal. ¦ý¥Ñ M ¬O maximal ideal ªº°²³]§Ú­Ìª¾ M + $ \bigl($a$ \bigr)$ ¤£¬O R ªº nontrivial proper ideal. ´«¥y¸Ü»¡ M + $ \bigl($a$ \bigr)$ = R. §Q¥Î 1 $ \in$ R = M + $ \bigl($a$ \bigr)$, §Ú­Ìª¾¦s¦b m $ \in$ M, r $ \in$ R º¡¨¬ 1 = m + r . a. §O§Ñ¤F§Ú­Ì¬O­n°Q½× R/M ªº¤¸¯À, ©Ò¥H¥Ñ¤W¦¡¥H¤Î¦b R/M ¤¤ $ \overline{m}$ = $ \overline{0}$ §Ú­Ì¦³

$\displaystyle \overline{1}$ = $\displaystyle \overline{m}$ + $\displaystyle \overline{r\cdot a}$ = $\displaystyle \overline{r}$ . $\displaystyle \overline{a}$.

¦]¦¹ $ \overline{a}$ ¬O R/M ªº unit, ¬Gª¾ R/M ¬O¤@­Ó field.

¤Ï¤§­Y R/M ¬O¤@­Ó field, §Ú­Ì·QÃÒ M ¬O R ªº¤@­Ó maximal ideal. ¦A¦¸±j½Õ§Ú­Ì¤£¬O­nÃÒ©ú¥ô·N R ¤¤ªº nontrivial proper ideal ³£º¡¨¬ I $ \subseteq$ M, ¦Ó¬O­nÃÒ©ú¤£¥i¯à M $ \subsetneq$ I. §Ú­Ì­n¥Î¤ÏÃÒªk: °²³] M ¤£¬O maximal ideal, §Y¦s¦b¤@­Ó nontrivial proper ideal I º¡¨¬ M $ \subsetneq$ I. ¥Ñ M $ \subseteq$ I ¦ý M$ \ne$I ª¾¦s¦b a $ \in$ I ¦ý a $ \not\in$M, ¤]´N¬O»¡¦b R/M ¤¤ $ \overline{a}$$ \ne$$ \overline{0}$. ¦ý R/M ¬O¤@­Ó field, ¬G¦s¦b r $ \in$ R ¨Ï±o

$\displaystyle \overline{r}$ . $\displaystyle \overline{a}$ = $\displaystyle \overline{r\cdot a}$ = $\displaystyle \overline{1}$.

³o§i¶D§Ú­Ì 1 - r . a $ \in$ M, ¤]´N¬O»¡ 1 = m + r . a ¨ä¤¤ m $ \in$ M. ¥Ñ©ó a $ \in$ I ¥B I ¬O¤@­Ó ideal, §Ú­Ìª¾ r . a $ \in$ I. ¦]¦¹¥Ñ m $ \in$ M $ \subseteq$ I ±o 1 = m + r . a $ \in$ I. Lemma 6.2.4 §i¶D§Ú­Ì 1 $ \in$ I ªí¥Ü I = R, ¦¹©M I ¬O nontrivial proper ideal ¬Û¥Ù¬Þ, ¬Gª¾ M ¬O maximal ideal. $ \qedsymbol$

Remark 6.5.12   §Ú­Ì¥i¥H§Q¥Î Correspondence ©w²z«Ü§ÖªºÃÒ©ú Theorem 6.5.11. ¦^ÅU¤@¤U Corollary 6.3.7 §i¶D§Ú­Ì R/M ¤¤ªº ideal ³£¬O¥Ñ¤¶©ó R ©M M ¶¡ªº ideal ©Ò§Î¦¨. ¦]¦¹­Y M ¬O maximal ideal, ªí¥Ü¤¶©ó R ©M M ¶¡©Ò¦³ªº ideal ¥u¦³ R ©M M. ´«¥y¸Ü»¡ R/M ¤¤¥u¦³ R/M ©M M/M = $ \bigl($$ \overline{0}$$ \bigr)$ ³o¨â­Ó ideal ¦Ó¨S¦³ nontrivial proper ideal, ©Ò¥H¥Ñ Proposition 6.5.5 ª¾ R/M ¬O¤@­Ó field. ¥t¤@¤è­±¦pªG R/M ¬O¤@­Ó field, ¦P¼Ëªº¥Ñ Proposition 6.5.5 §Ú­Ìª¾ R/M ¨S¦³ nontrivial proper ideal. ¦]¦¹¥Ñ§Ú­Ì¦b Remark 6.3.6 ¤¤´£¨ìªº¤ñ¸û±j(¦³°ß¤@©Ê)ªº Correspondence ©w²zª¾¨S¦³¨ä¥Lªº ideal ¤¶©ó R ©M M ¤§¶¡, ¬G±o M ¬O maximal ideal.

§Ú­Ìª¾¹D¦b¤@­Ó field ¤¤«D 0 ªº¤¸¯À³£¬O unit, µM¦Ó Lemma 5.3.7 §i¶D§Ú­Ì¤@­Ó unit µ´¤£·|¬O zero divisor, ©Ò¥H§Ú­Ìª¾¹D¤@­Ó field ¨Æ¹ê¤W¬O¤@­Ó integral domain. ²­Y R/M ¬O¤@­Ó field, «h R/M ¬O¤@­Ó integral domain. ©Ò¥H¥Ñ Theorem 6.5.7 ©M Theorem 6.5.11 ¥i±o¥H¤U¤§µ²ªG:

Corollary 6.5.13   ­Y R ¬O¤@­Ó commutative ring with 1, «h R ¤¤ªº maximal ideal ³£¬O prime ideal.

ª`·N Corollary 6.5.13 ¤Ï¹L¨Ó¨Ã¤£¤@©w¹ï. ¨Ò¦p¦b $ \mathbb {Z}$ ¤¤§Ú­Ìª¾ $ \mathbb {Z}$/$ \bigl($0$ \bigr)$ $ \simeq$ $ \mathbb {Z}$, ¦ý $ \mathbb {Z}$ ¬O integral domain «o¤£¬O field, ©Ò¥Hª¾ $ \bigl($0$ \bigr)$ ¬O $ \mathbb {Z}$ ªº prime ideal ¦ý¤£¬O maximal ideal.


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