nª`·Nªº¬O: ¦]¬° a, b R, ©Ò¥H³o¸Ì a + b, a . b ¬O¦b R ¤¤ªº¥[ªk©M¼ªk; ¦Ó (a),(b) R', ©Ò¥H (a) + (b), (a) . (b) ¬O¦b R' ¤¤ªº¥[ªk©M¼ªk. ²³æ¦a»¡: ¤@Ó±q R ¨ì R' ªº ring homomorphism, ¬O¥[ªkªº group homomorphism ¦A¥[¤W«O«ù¼ªkªº¹Bºâ. ©Ò¥H¤@¯ë¨Ó»¡¦³Ãö©ó group homomorphism ªº©Ê½è³£¥i¥Hª½±µ®M¥Î¦b ring homomorphism ¤W. ¤ñ¤è»¡¥Ñ Lemma 2.5.2 ª¾ (0) = 0 (¨ä¤¤ ¸Ì±ªº 0 ¬O R ªº 0, ¥t¤@Ó 0 ¬O R' ªº 0) ¥B (- a) = - (a). ¦]¦¹¥H«ánpºâ (a - b) ®É¥Ñ©ó
¦b group homomorphism ¤¤§Ṳ́¶²Ð¤F¨âÓ«nªº¶°¦X image ©M kernel, ¦b ring homomorphism ³o¨âÓ¶°¦X¤´µM«Ü«n. §Ú̦A¦^ÅU¤@¤U¥¦Ìªº©w¸q.
ª`·N³o¸Ì kernel ¤¤ªº 0 ¬O R' ¥[ªkªº identity. ¦b group homomorphism ¤¤ image ©M kernel ¤À§O¬O¹ïÀ³°ìªº subgroup ©M©w¸q°ìªº normal subgroup. ¤j®aÀ³¤£Ãø²q¥X¦b ring homomorphism ¥¦Ìªº©Ê½è§a!
Y (a),(b) im(), ¨ä¤¤ a, b R, «h (a) . (b) = (a . b). ¤S¦] a . b R, ¬G (a) . (b) im(). ¦]¦¹¥Ñ Lemma 5.4.2 ª¾ im() ¬O R' ªº subring.
¦Ü©ó ker() ¬O R ªº ideal, §ÚÌ¥unÃÒ: ¹ï¥ô·Nªº r R ©M a ker() ¬Ò¦³ r . a ker() ¤Î a . r ker(). µM¦Ó (r . a) = (r) . (a) = (r) . 0, §Q¥Î Lemma 5.2.1 ª¾ (r . a) = 0 ¬G r . a ker(). ¦P²z±o a . r ker(). ¦]¦¹¥Ñ Lemma 6.1.2 ª¾ ker() ¬O R ªº ideal.
¦b Lemma 2.5.6 ¤¤§Ú̪¾¹D¥i¥H¥Î kernel ¨Ó§PÂ_¤@Ó group homomorphism ¬O§_¬°¤@¹ï¤@, ¬JµM ring homomorphism ¦b¥[ªk¤§¤U¬O group homomorphism ©Ò¤U±ªº Lemma ·íµM¦¨¥ß.
ÁA¸Ñ¤F ring homomorphism, ±µ¤U¨Ó§ÚÌ¨Ó½Í ring homomorphism ªº correspondence ©w²z. ¦^ÅU¤@¤U group homomorphism ¤¤ªº correspondence ©w²z´yz¤F¨âÓ group ªº subgroup ©M normal subgroup §Q¥Î group homomorphism ©Ò±o¨ìªº¹ïÀ³Ãö«Y. ¹ï ring homomorphism §Ṳ́]¦³Ãþ¦üª¬ªp.
¦pªG¤S°²³] S' ¬O R' ªº ideal. «h«e±©Ò©wªº S ¤]·|¬O R ªº ideal.
Y a ker(), «h (a) = 0. ¦] 0 S' ¬G a S. ©Ò¥H ker() S. (³o³¡¤ÀªºÃÒ©ú¤]¤£»Ý onto.)
²¦bÃÒ (S) = S'. º¥ýÃÒ©ú (S) S' ³o³¡¥÷¬O®e©öªº. ¥Dn¬O¦] (S) ªº¤¸¯À³£¬O (a) ³oºØ§Î¦¡, ¨ä¤¤ a S. ¥Ñ©w¸q a S, ªí¥Ü (a) S'. ¬G (S) ªº¤¸¯À³£¸¨¦b S' ¤¤. «Ü¦h¦P¾Ç³£·|»¬° S' ªº¤¸¯À¤]·|¦b (S) ¤¤; ¤@¯ë³o¬O¤£¤@©w¹ïªº. ¦]¬°¦b¤@¯ëªº±¡ªp b S' ¤£¥Nªí¦³¤¸¯À a R ¨Ï±o (a) = b. ³o¸Ì§ÚÌ´Nn¥Î¨ì onto ªº©Ê½è¤F. ¦]¬° ¬O onto ¬G¹ï¥ô·N b S' R' ³£¥i§ä¨ì a R ¨Ï±o (a) = b. ¬JµM (a) = b S', ³o¤@Ó a ¤]´N¦b S ¤¤¤F. ©Ò¥H b = (a) (S), ¤]´N¬O»¡ S' (S). ¥Ñ¦¹±oÃÒ S' = (S).
³Ì«á§ÚÌnÃÒ©úY S' ¬O R' ªº ideal, «h S ¤]¬O R ªº ideal. ¹ï¥ô·Nªº r R, a S ¬Ò¦³ (r . a) = (r) . (a). ¥Ñ©ó (r) R' ¥B (a) S' ¤Î S' ¬O R' ªº ideal, §Ú̦³ (r) . (a) S'. ¬G r . a S, ¦P²z±o a . r S. ©Ò¥H S ¬O R ªº ideal.
¦A¦¸±j½Õ³oÓ©w²z¤¤°£¤F (S) = S' »Ý¥Î¨ì ¬O onto ¥ , ¨ä¥L©Ê½è¨Ã¤£»Ý onto ªº°²³].
Correspondence Theorem ³Ì±`¥Îªº±¡ªp¬O·í I ¬O R ªº¤@Ó ideal, ¦Ó ¬O R ¨ì R/I ªº ring homomorphism ¨ä¤¤¹ï¥ô·Nªº a R, ©w¸q (a) = .
·í S' ¬O R/I ªº ideal ®É, «h S ¤]·|¬O R ªº ideal.
¦AÃÒ©ú ¬O onto ªº, ¨Æ¹ê¤W¹ï©Ò¦³ y R/I ³£¬O y = , ¨ä¤¤ a R ³oºØ§Î¦¡. ¬G¿ï a R ±a¤J ±o (a) = = y. ±oÃÒ ¬O onto.
ker() ¬O¬Æ»ò©O? Y a ker() «h (a) = , ¦ý¥Ñ ªº©w¸q (a) = . ¬G¥Ñ = , ±o a I. ¤Ï¤§Y a I, «h (a) = = , ¬G a ker(). ¥Ñ¦¹±o ker() = I.
²¦b Correspondence Theorem ¤¤ªº±ø¥ó³£§ä¨ì¤F, ©Ò¥H§Q¥Î Theorem 6.3.5 ª¾¥ô¨ú R/I ¤¤ªº¤@Ó subring (©Î idealS'), ¦b R ¤¤³£¥i¥H§ä¨ì¤@Ó subring (©Î ideal) S ²Å¦X I = ker() S ¥B (S) = S/I = S'.
¦³³h®Ñ¤]ºÙ Corollary 6.3.7 ¬° Correspondence Theorem. ¥¦§i¶D§ÚÌ R/I ¤¤ªº subring (©Î ideal) ³£¬Oªø S/I ³oºØ§Î¦¡, ¨ä¤¤ S ¬O R ªº subring (©Î ideal) ¥B I S.