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¤U¤@­¶: Polynomials over unique factorization ¤W¤@­¶: Unique Factorization Domain «e¤@­¶: Unique Factorization Domain

Unique factorization domain ªº°ò¥»©Ê½è

¹ï©ó¤@­Ó unique factorization domain §Ú­Ì¥i¥H¹³³B²z¾ã¼Æªº±¡ªp¨Ó³B²z¤@¨Ç¦³Ãö©ó divisor ªº°ÝÃD. ¤ñ¤è»¡¦b $ \mathbb {Z}$ ¤¤­n§ä¨ì¨â¤¸¯À a, b ªº greatest common divisor °£¤F§Q¥ÎÁÓÂà¬Û°£ªk¥ , §Ú­ÌÁÙ¥i±N a, b °µ½è¦]¼Æ¤À¸Ñ¥H¨D¥X greatest common divisor.

¹ï©ó¤@¯ëªº unique factorization domain R ¥Ñ©ó R ¤£¤@©w¬O Euclidean domain, ©Ò¥HµLªk¥ÎÃþ¦üÁÓÂà¬Û°£ªkªº¤èªk¨D greatest common divisor. µM¦Ó­Y a, b $ \in$ R, §Ú­Ì¥i¥H§Q¥Î unique factorization domain ªº©Ê½è±N a, b ¤À¸Ñ¦¨

a = u . p1n1 ... prnr,    ¤Î    b = v . p1m1 ... prnr, (8.1)

¨ä¤¤ u, v ¬O R ¤¤ªº units, p1,..., pr ¬O R ¤¤¨â¨â¤£ associates ªº irreducible elements, ¦Ó¹ï¥ô·Nªº i $ \in$ {1,..., r}, ni ©M mi ³£¬O«D­t¦ý¤£¦P®É¬° 0 ªº¾ã¼Æ. ³o¸Ì§Ú­Ì¥i¥H­n¨D p1,..., pr ³£¥X²¦b a, b ªº½è¦]¼Æªº¤À¸Ñ¤¤¥D­n¬O§Ú­Ì®e³ ni ©Î mi ¬° 0, ©Ò¥H­Y pi | a ¦ý pi$ \nmid$b §Ú­Ì¥O mi = 0. ¤Ï¤§­Y pj | b ¦ý pj$ \nmid$a, «h¥O nj = 0. ¦]¦¹­Y¥O

d = p1t1 ... prtr,

¨ä¤¤ ti = min{ni, mi}, §Ú­Ì¥i¥HÃÒ©ú d ¬O a, b ªº greatest common divisor.

Proposition 8.4.1   °²³] R ¬O¤@­Ó unique factorization domain ¥B a1,..., an ¬O R ¤¤ªº«D 0 ¤¸¯À, «h a1,..., an ªº greatest common divisor ¦s¦b.

µý ©ú. §Q¥Î Lemma 8.1.6 §Ú­Ì¥u­nÃÒ©ú R ¤¤¥ô·N¨â­Ó«D 0 ¤¸¯À a ©M b ªº greatest common divisor ¦s¦b§Y¥i.

­º¥ý§Ú­Ì±N a, b ªº¤À¸Ñ¼g¦¨¦¡¤l (8.1) ªº§Î¦¡, ¥B¥O

d = p1t1 ... prtr,

¨ä¤¤ ti = min{ni, mi}. §Ú­Ì­nÃÒ©ú d ¬O a, b ªº greatest common divisor.

­º¥ý¥Ñ ti$ \le$mi ¥H¤Î ti$ \le$ni, $ \forall$ i = 1,..., r, «Ü®e©ö±oª¾ d | a ¥B d | b. ¦]¦¹ª¾ d ¬O a, b ªº common divisor. ²­Y c ¬O a, b ªº¤@­Ó common divisor, °²³] p ¬O¤@­Ó irreducible element ¥B p | c, «h¥Ñ p | a ¥B p | b ª¾ p ¤@©w©M p1,..., pr ¤¤¬Y¤@­Ó pi associates. ³o§i¶D§Ú­Ì¦b c ªº¤À¸Ñ¤¤¤£¥i¯à¥X²©M p1,..., pr ¤£ associates ªº irreducible divisor, ¤]´N¬O»¡§Ú­Ì¤]¥i±N c ¤À¸Ñ¦¨

c = w . p1s1 ... prsr,

¨ä¤¤ w ¬O unit ¥B si ¬O«D­t¾ã¼Æ. ²¦pªG¦³­Ó i ²Å¦X si > ni, ¬°¤F¤è«K´N°²³] s1 > n1 §a! §Q¥Î p1s1 | c ¥H¤Î c | a ª¾ p1s1 | a. ´«¨¥¤§

p1s1 - n1 | p2n2 ... prnr.

¥Ñ s1 - n1$ \ge$1 ±o

p1 | p2n2 ... prnr.

µM¦Ó p1 ¬O prime, ³oªí¥Ü p1 ©M p2,..., pr ¤¤¬Y­Ó pi associates. ³o©M·íªì°²³] p1,..., pr ¨â¨â¤£ associates ¬Û¥Ù¬Þ, ¬G±o si$ \le$ni, $ \forall$ i = 1,..., r. ¦P²z si$ \le$mi, $ \forall$ i = 1,..., r. ¬G±oª¾¹ï©Ò¦³ªº i = 1,..., r ¬Ò¦³ si$ \le$min{ni, mi} = ti. ¤]´N¬O»¡ c | d. ¬Gª¾ d ¬O a, b ªº greatest common divisor. $ \qedsymbol$

¦b«e­±´X¸`¤¤­nÃÒ©ú¤@­Ó integral domain ¬O¤@­Ó unique factorization domain, §Ú­Ì³£¥hÃÒ©ú³o­Ó integral domain ¤¤ªº irreducible elements ©M prime elements ¬O¤@¼Ëªº. ¨Æ¹ê¤W, ¦b unique factorization domain ¤¤ irreducible element ©M prime element Á`¬O¬Û¦Pªº.

Proposition 8.4.2   ­Y R ¬O¤@­Ó unique factorization domain, «h R ¤¤ªº irreducible elements ©M prime elements ¬O¬Û¦Pªº.

µý ©ú. §Ú­Ì¤wª¾¦b¤@­Ó integral domain ¤¤ prime element ·|¬O irreducible element (Lemma 8.1.8). ©Ò¥H§Ú­Ì¥u­nÃÒ©ú irreducible element ¤]·|¬O prime element.

°²³] p $ \in$ R ¬O¤@­Ó irreducible element ¥B p | a . b, ¨ä¤¤ a, b $ \in$ R. ¥Ñ°²³]ª¾¦s¦b h $ \in$ R º¡¨¬ a . b = h . p. ­º¥ý§Ú­Ì±N a, b ¥Î¦¡¤l (8.1) ªº§Î¦¡¤À¸Ñ, ¦]¦¹¦³

a . b = (u . v) . p1n1 + m1 ... prnr + mr.

§Q¥Î R ¬O unique factorization domain, ¥Ñ a . b ªº¤À¸Ñª¾ p ¤@©w©M p1,..., pr ¤¤¬Y¤@­Ó pi associates. µM¦Ó ni ©M mi ¤£¦P®É¬° 0, ¤]´N¬O»¡ ni$ \ne$ 0 ©Î mi$ \ne$ 0. ­Y ni$ \ne$ 0, «hª¾ p | a, ¦Ó­Y mi$ \ne$ 0 «h¦³ p | b. ¬G±oÃÒ p ¬O prime element. $ \qedsymbol$


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¤U¤@­¶: Polynomials over unique factorization ¤W¤@­¶: Unique Factorization Domain «e¤@­¶: Unique Factorization Domain
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