¾ã¼Æ¤¤³Ì°ò¥»ªº©w²zÀ³¸Ó´N¬O¾ã¼Æªº¾l¼Æ©w²z Euclid's Algorithm, ´X¥G©Ò¦³¾ã¼Æªº°ò¥»©Ê½è³£¬O¥Ñ¥¦±À¾É¥X¨Óªº. ¨ä¹ê§Ú̦b«e±¤w¸g¥Î¹L³oÓ©w²z¦n´X¦¸¤F, ¤£¹L¬°¤F§¹¾ã©Ê§ÚÌÁÙ¬Oµ¹¤@ÓÃÒ©ú.
º¥ý¦Ò¼ W = {m - t . n | t } ³o¤@Ó¶°¦X. ¦]¬° t ¥i¨ú¥ô¦ó¾ã¼Æ, «Ü®e©ö´N¬Ý¥X W ¤@©w¥]§t¤@¨Ç«Dtªº¾ã¼Æ. ¥O r ¬O W ¤¤³Ì¤pªº«Dtªº¾ã¼Æ, ¦]¬° r W, ¥Ñ©w¸qª¾¦s¦b h º¡¨¬ r = m - h . n. §Ú̳̥Dnªº¥Øªº´N¬OnÃÒ©ú 0r < n.
°²³] r ¤£¦X§Ú̪º±ø¥ó, ¤]´N¬O»¡ rn (§O§Ñ¤F r ¬O«Dt¾ã¼Æªº°²³]). Y¦p¦¹, §ÚÌ¥i±N r ¼g¦¨ r = n + r', ¨ä¤¤ r' 0. ¦]¦¹§Q¥Î
nª`·N Theorem 7.1.1 ªºÃÒ©ú§Ú̥Ψì¾ã¼Æ¤W¥i¥H±Æ§Çªº well-ordering principle, ¦]¦¹ÁöµMÃÒ©ú«Ü²³æ, ¦ý¨Ã¤£¯àª½±µ®M¥Î¨ì¤@¯ëªº ring. ¤]´N¬O»¡, ¤@¯ëªº ring ¤£¤@©w¦³©Ò¿×ªº Euclid's Algorithm. ±N¨Ó§ÚÌ·|¬Ý¨ì¤@¨Ç¯S®íªº integral domain ¤]¦³©Ò¿×ªº Euclid's Algorithm. ³o¼Ëªº integral domain §ÚÌ·|µ¹¥¦¤@Ó¦WºÙ: ºÙ¬° Euclidean domain.
±µ¤U¨Ó§ÚÌ´N¨Ó¬Ý¬Ý Theorem 7.1.1 ªºÅ]¤O¦³¦h¤j§a!
¤¤ªº trivial ideal Z ©M {0}, ¤À§O¥Ñ 1 ©M 0 ¥Í¦¨, ©Ò¥H³£¬O principle ideal. ¦]¦¹§ÚÌ¥un¦Ò¼ ¤¤ nontrivial proper ideal ´N¥i. °²³] I ¬O ªº¤@Ó nontrivial proper ideal, ¥Ñ©ó I{0}, ¬G¦s¦b b 0, ¥B b I. ¥Ñ©ó I ¬O ideal, - b ¤]¦b I ¤¤, ¦]¦¹§Ú̪¾ I ¤¤¥²¦s¦b¥¿¾ã¼Æ. ²¥O a I ¬O I ¤¤³Ì¤pªº¥¿¾ã¼Æ, §ÚÌnÃÒ©ú I = a.
º¥ý a I, ©Ò¥H¹ï¥ô·Nªº h ¬Ò¦³ h . a I, ¬Gª¾ a I. ¦]¦¹§Ú̶ȳѤUnÃÒ I a, ´«¥y¸Ü´N¬OnÃÒ©ú I ¤¤ªº¤¸¯À³£¬O a ªº¿¼Æ. ¥ô¨ú m I «ç»ò»¡ m ¬O a ªº¿¼Æ©O? (·íµM´N¬O®³ m °£¥H a ¬Ý¬Ý¾l¼Æ¬O¤°»ò¤F.) §Q¥Î Theorem 7.1.1, §Ú̪¾¦s¦b h, r , 0r < a º¡¨¬ r = m - h . a. ¥Ñ©ó m I ¥B h . a I, §Q¥Î I ¬O ideal ª¾ r = m - h . a I. ¦ý¤wª¾ a ¬O I ¤¤³Ì¤pªº¥¿¾ã¼Æ, ¬G±o r = 0, §Y m = h . a a. ¤]´N¬O»¡ I a.
§ÚÌ´¿´£¿ô¹L, ¨Ã¤£¬O©Ò¦³ªº ring ¥¦ªº ideal ³£·|¬O principle ideal. ¦pªG¤@Ó integral domain ¥¦ªº ideal ³£¬O principle ideal, ³o¼Ë¯S§Oªº integral domain §Ú̺٤§¬° principle ideal domain. ª`·N¥H¤W ¬O principle ideal domain (Theorem 7.1.2) ªº©Ê½è, ¬O¥Ñ ¬O Euclidean domain (Theorem 7.1.1) ³oөʽè±À¾É¥X¨Óªº.
³o¤@¸`§ÚÌ¥Dn¬O½Í¾ã¼Æ¤W¤¸¯Àªº¤À¸Ñ, ©Ò¥HÁÙ¬Oµ¹¦]¼Æ, ¤½¦]¼Æ©M³Ì¤j¤½¦]¼Æ¤U¤@Ó©w¸q.
¤@¯ë³£¬O§Q¥Î©Ò¿×ªºÁÓÂà¬Û°£ªk±N¨âӼƪº greatest common divisor ¨D¥X, ¦b³o¸Ì§Ú̱N§Q¥Î Theorem 7.1.2 §ä¨ì greatest common divisor ¨Ã±o¨ì¨ä°ò¥»©Ê½è.
±µµÛ§ÚÌnÃÒ©ú³oÓ d ¬O a, b ªº greatest common divisor. º¥ý·íµM¬OnÃÒ d ¬O a, b ªº common divisor. µM¦Ó¦] a a a + b = d, ¬Gª¾¦s¦b r ¨Ï±o a = r . d. ¤]´N¬O»¡ d | a. ¦P²z, ¥Ñ b d ¥i±o d | b. ¬Gª¾ d ¬O a, b ªº common divisor.
¨º¬°¬Æ»ò d ·|¬O a, b ªº common divisor ¤¤³Ì¤jªº©O? ¥Ñ©ó d d = a + b, §Ú̪¾¹D¦s¦b m, n ¨Ï±o d = m . a + n . b. µM¦ÓY c ¬O a, b ªº common divisor, §Y c | a ¥B c | b, ª¾¦s¦b r, s ¨Ï±o a = r . c ¥B b = s . c. ¦]¦¹±o
Proposition 7.1.4 ¤£¥u§i¶D§Ú̦p¦ó§ä¨ì greatest common divisor, ¨Æ¹ê¤W¦bÃÒ©ú¤¤§Ṳ́]ÃÒ±o greatest common divisor ªº¨âÓ«n©Ê½è.
±µ¤U¨Ó§ÚÌn½Í¾ã¼Æªº¤À¸Ñ¤¤³Ì°ò¥»ªº¤¸¯À: ½è¼Æ. ¤j®a³£ª¾¹D¤@Ó½è¼Æ p ´N¬O¦]¼Æ¥u¦³ 1 ©M¥»¨ªº¼Æ. §Q¥Î³oөʽè§ÚÌ¥i±o¨ìY p | a . b «h p | a ©Î p | b ³oөʽè, ¦]¦¹¤j®a³£·|®³³o¨âºØ©Ê½è¨Ó§P§O¤@ӼƬO§_¬°½è¼Æ. ¤£¹L¦b¤@¯ëªº ring ³o¨âºØ©Ê½è¬O«Ü¤£¤@¼Ëªº, ©Ò¥H§Ú̥Τ£¦Pªº¦W¦r¨ÓºÙ©I.
«ÜÅãµM³o¨âºØ©w¸q¬O¤£¤@¼Ëªº, ¤£¹L¤U¤@Ó©w²z§i¶D§Ú̦b¾ã¼Æ¤¤³o¨âºØ©w¸qªº¤¸¯À¬O¬Û¦Pªº. ¤]¦]¦p¦¹¦b¾ã¼Æ¤¤§ÚÌ´N²Î¤@ºÙ¤§¬°½è¼Æ (prime).
¤Ï¤§, Y¤wª¾ p ¬O¤@Ó prime element §ÚÌnÃÒ©ú p ¬O irreducible. ¤]´N¬OÃÒ©úY d | p, «h d = ±1 ©Î d = ±p. µM¦Ó d | p ªí¥Ü¦s¦b r º¡¨¬ p = d . r, ¤]´N¬O»¡ p | d . r. ¬G¥Ñ p ¬O prime ªº°²³], §Ú̱o p | d ©Î p | r. ·í p | d ®É, ¥Ñì¥ý°²³] d | p ª¾ d = ±p. ·í p | r ®É, ªí¥Ü¦s¦b s º¡¨¬ r = s . p. ¬G¥Ñ p = d . r = d . (s . p) ±o d . s = 1. ¦] d, s , ¬G d . s = 1 ªí¥Ü d = ±1.
³Ì«á§Ų́Ӭݾã¼Æ³Ì°ò¥»¤]³Ì«nªº°ß¤@¤À¸Ñ©w²z. ¥Ñ©ó¥¿¾ã¼Æ©Mt¾ã¼Æªº¤À¸Ñ¥u®t¤@Ót¸¹, §ÚÌ¥u»Ý¦Ò¼¥¿¾ã¼Æªº±¡ªp.
¦pªG a ¥i¥H¤À¸Ñ¦¨¥t¥ ªº§Î¦¡ a = q1m1 ... qsms, ¨ä¤¤ qi ¬O¬Û²§ªº prime, «h r = s ¥B¸g¹LÅÜ´«¶¶§Ç¥i±o pi = qi, ni = mi, i {1,..., r}.
º¥ý¨Ó¬Ý¦s¦b©Ê: ²³æ¨Ó»¡¦s¦b©Ê´N¬OnÃÒ©ú¨C¤@Ó¤j©ó 1 ªº¾ã¼Æ³£¥i¥H¼g¦¨¦³¦hÓ(¥i¥H¬Û¦P) prime ªº¼¿n. ¦pªG a ¥»¨¬OÓ prime, «h a = p1 (§Y r = 1, n1 = 1), ±oÃÒ¦s¦b©Ê. ¦pªG a ¤£¬O prime ©O? ¥Ñ Proposition 7.1.7 ª¾ a ¤£¬O irreducible, ¤]´N¬O»¡¦s¦b a1, b1 ¥B a11, b11 º¡¨¬ a = a1 . b1. ±µ¤U¨Ó´N¬O¬Ý a1, b1 ¬O¤£¬O prime ¤F. ¦pªG¨ä¤¤¦³¤@Ó¤£¬O prime, §ÚÌ´NÄ Äò¤À¸Ñ¤U¥hª½¨ì±o¨ì prime ¬°¤î. ³oÓ¹Lµ¤@©w·|°±¤U¨Ó¦]¬°¨C¦¸¤À¸Ñ«á±oªº¼Æ¶V¨Ó¶V¤p. ·íµM³Ì«á´N¥i¥H±N a ¼g¦¨¤@¨Ç prime ªº¼¿n¤F. ³o¼ËªºÃÒ©ú¤è¦¡, ¬Û«H¤j®a·|¦³¤@ºØ»¡¤£²M·¡ªº·Pı, ©Ò¥H§ÚÌÁÙ¬O¥Î¤ñ¸û¼Æ¾Çªº¤èªk¨ÓÃÒ©ú. ·í a = 2 ®É¥Ñ©ó 2 ¬O prime, ©Ò¥H¦b³o±¡ªp¦s¦b©Ê¬O¹ïªº. ±µµÛ°²³]¹ï©Ò¦³¤¶©ó 2 ©M a - 1 ªº¾ã¼Æ¦s¦b©Ê¬O¹ïªº. ¦pªG a ¬O prime, ¨º¦s¦b©Ê¦ÛµM¦¨¥ß, ¦pªG a ¤£¬O prime, «h¥Ñ Proposition 7.1.7 ª¾ a = a1 . b1 ¨ä¤¤ a1, b1 ¥B 1 < a1 < a ¤Î 1 < b1 < a. ¬G§Q¥ÎÂk¯Ç°²³]ª¾ a1 ©M b1 ³£¥i¼g¦¨¦³¦hÓ prime ªº¼¿n, ©Ò¥H±oÃÒ a ¤]¥i¥H¼g¦¨¦³¦hÓ prime ªº¼¿n.
§Ų̵́M¥ÎÂk¯ÇªkÃҰߤ@©Ê, °²³]
¦pªG¤@Ó integral domain ¦³©M ¤@¼Ë¨CÓ¤¸¯À³£¥i¥H°ß¤@¼g¦¨¤@¨Ç irreducible element ªº¼¿nªº©Ê½è, §ÚÌ«KºÙ¦¹ integral domain ¬°¤@Ó unique factorization domain.