¤U¤@¶: ½u©Ê¥N¼ÆªºÀ³¥Î
¤W¤@¶: ªì¯Å Field ªº©Ê½è
«e¤@¶: Field ªº°ò¥»©Ê½è
¹ï¤@¯ëªº field F, Y a F, ¥Ñ©ó 1 F, ¬G¹ï¥ô·Nªº
n
§Ú̦³
= () . a. |
(9.1) |
nª`·N¦b³o¸Ì 1 ¥[ n ¦¸¨Ã¤£µ¥©ó n, ³o¬O¥Ñ©ó³o¸Ìªº 1 ¬O F
¤¤ªº 1 ¨Ã¤£¬O¦ÛµM¼Æ
¤¤ªº 1. ¨Ò¦p¤W¨Ò¤¤
¬O
/5 ¤¤ªº 1, ¦ý
¦Ó¦b
¤¤ 5 ¬O¤£µ¥©ó 0 ªº. ©Ò¥H§Ṳ́£¯à§â¦¡¤l (9.1) ¼g¦¨
=
n . a.
¤£¹L¬°¤F¤è«K, ¹ï¥ô·N a F ¥B
n §Ú̥Πna ¨Óªí¥Ü a
¦Û¤v¥[¦Û¤v n ¦¸, ¤]´N¬O»¡
=
na.
§Æ±æ¤£·|³y¦¨¤j®aªº§xÂZ. ¦]¦¹§ÚÌ¥i¥H±N¦¡¤l
(9.1) ¼g¦¨
na =
= (
)
. a = (
n1)
. a.
µý ©ú.
¦Ò¼
:
F ¨ä¤¤
(0) = 0, ¥B¹ï¥ô·N
n ,
(
n) =
n1,
(-
n) =
n(- 1). §Y
ª`·N³o¸Ìªº 1 ¬O
F ¤¤ªº 1, ¦Ó -1 ¬O
F ¤¤ 1 ªº¥[ªk
inverse. «Ü®e©öÀˬd
¬O¤@Ó±q
¨ì
F ªº ring
homomorphism.
²¦Ò¼ ªº kernel. ¥Ñ ring ªº 1st isomorphism theorem (Theorem
6.4.2) §Ú̦³
µM¦Ó
im(
) ·|¬O
F ªº¤@Ó subring (Lemma
6.3.3), ¬G¥Ñ
F
¬O integral domain (Lemma
9.1.1) ª¾
im(
) ¤]¬O¤@Ó
integral domain. ´«¥y¸Ü»¡
/ker(
) ¬O¤@Ó integral domain.
¥t¤@¤è±
ker(
) ·|¬O
ªº¤@Ó ideal (Lemma
6.3.3)
¬G§Q¥Î Theorem
6.5.7 ª¾
ker(
) ¬O
ªº¤@Ó prime
ideal. ¦]
¬O¤@Ó principle ideal domain, ¬G¦s¦b
a º¡¨¬
ker(
) =
a. §Q¥Î Lemma
8.1.9 §Ú̪¾
a = 0 ©Î
a =
p, ¨ä¤¤
p ¬O
¤¤ªº¤@Ó prime.
(1)
ker() = 0 ªº±¡§Î: ¦¹®É¦]¹ï¥ô·Nªº
n , ¬Ò¦³
n1 0 (¦]
n ker()), ¬Gª¾¹ï¥ô·Nªº a F ¥B a 0, ¦] F ¬O integral domain, ¬Ò¦³
na = (
n1)
. a0.
(2)
ker() = p ªº±¡§Î: ¦¹®É¦]
p ker(), §Ú̦³
p1 = 0. ¬G±o¹ï¥ô·Nªº a F ¬Ò¦³
pa = (p1) . a = 0.
¦b Lemma 9.2.1 ¤¤ªº 0 ©Î p ¹ï field
ªº¤ÀÃþ¤W¬O«Ü«nªº, ¦]¦¹§Ú̦³¥H¤U¤§©w¸q.
Definition 9.2.2
°²³]
F ¬O¤@Ó field. Y¹ï¥ô·Nªº
n ¥B
a F {0} ¬Ò¦³
na 0, «hºÙ
F ªº
characteristic ¬O
0. °O¬°
char(
F) = 0. ¤Ï¤§Y¦s¦b
p ¬O
¤¤ªº prime
¨Ï±o¹ï¥ô·Nªº
a F ¬Ò¦³
pa = 0, «hºÙ
F ªº
characteristic
¬O
p. °O¬°
char(
F) =
p.
¨Ò¦p¦³²z¼Æ©Ò¦¨ªº field
ªº characteristic ´N¬O 0. ¤S¨Ò¦p¦b
Example 9.1.3 ¤¤ªº
/5 ´N²Å¦X¹ï¥ô·Nªº
a /5
¬Ò¦³ 5a = 0, ©Ò¥H§Ú̦³
char(/5) = 5.
nª`·N¥Ñ Lemma 9.2.1 §Ú̪¾Y F ¬O¤@Ó field, «h
char(F)
n¤£¬Oµ¥©ó 0 ´N¬Oµ¥©ó¤@Ó prime p. ¦pªG
char(F) = p 0, «h¦¹
p ¬Oº¡¨¬ pa = 0 ¨ä¤¤
a F {0} ªº³Ì¤pªº¥¿¾ã¼Æ. ¦]¬°Y
n ¥B na = 0, «h¥Ñ F ¬O integral domain ¥H¤Î
na = (n1) . a = 0
ª¾ n1 = 0. ¤]´N¬O»¡
n ker() = p.
³o§i¶D§ÚÌ np.
Y F ¬O¤@Ó field ¥B F ¥u¦³¦³¦hÓ¤¸¯À, «h§Ú̺٠F ¬°¤@Ó
finite field.
Lemma 9.2.3
Y
F ¬O¤@Ó finite field, «h¦s¦b¤@ prime
p ¨Ï±o
char(
F) =
p.
µý ©ú.
¥Ñ Lemma
9.2.1 §Ú̪¾
char(
F) = 0 ©Î
char(
F) =
p ¨ä¤¤
p
¬O¤@Ó½è¼Æ. §ÚÌn»¡©ú
char(
F) ¤£¥i¯à¬O 0. ¨ä¹ê¦pªG
char(
F) = 0,
ªí¥Ü«e±©wªº¨ºÓ ring homomorphism
:
F ²Å¦X
ker(
) =
0
, ¤]´N¬O»¡
¬O¤@¹ï¤@ªº. ´«¨¥¤§
im(
)
F. µM¦Ó
¦³µL½a¦hÓ¤¸¯À, ¬G±o¨ì
F ¤¤¦³¤@Ó subring ¨ä¤¸¯À¦³µL½a¦hÓ. ¦¹©M
F ¬O finite field
¬Û¥Ù¬Þ, ¬Gª¾
char(
F) =
p 0.
§Q¥Î Proposition 9.1.5 §ÚÌ¥i±o¥H¤U¦³Ãö©ó characteristic
ªº©Ê½è. ¥¦§i¶D§ÚÌ·í¨âÓ field ªº characteristic ¤£¬Û¦P®É,
¥¦Ì¤§¶¡¤£¥i¯à¦s¦b nontrivial ªº ring homomorphism.
Proposition 9.2.4
°²³]
F ©M
F' ¬O fields ¥B
F ©M
F' ¤§¶¡¦s¦b nontrivial ªº
ring homomorphism, «h
char(
F) = char(
F').
µý ©ú.
°²³]
:
FF' ¤£¬O¤@Ó trivial ªº ring homomorphism, ¥Ñ
Proposition
9.1.5 (1) ª¾
(1
F) = 1
F'. ¦]¦¹Y
char(
F) =
p 0, §Q¥Î
(
p1
F) =
(0) = 0
¥H¤Î
(
p1
F) =
(
) =
p(1
F) =
p1
F',
§Ú̱o
p1F' = 0.
¬Gª¾
char(
F')
0. µM¦ÓY
char(
F') =
qp, «h¦]
p ©M
q ¬Ò¬O½è¼Æ©Ò¥H¤¬½è, ¬G¦s¦b
m,
n ¨Ï±o
mp +
nq = 1.
¦]¦¹¥Ñ
p1
F' =
q1
F' = 0 ¥i±o
1F' = (mp + nq)1F' = 0,
³y¦¨¥Ù¬Þ. ¬Gª¾
char(
F) = char(
F').
¥t¥ Y
char(F) = 0, ¦¹®É¹ï¥ô·N
n ¬Ò¦³ n1F 0. §Q¥Î
Proposition 9.1.5 (2) ª¾
(n1F) 0. ´«¥y¸Ü»¡
³oªí¥Ü
char(
F') = 0.
³Ì«á§Ų́Ӭݷí
char(F) = p 0 ®É, ¦b¹Bºâ¤Wªº¤@Ó¯S®í©Ê½è.
Lemma 9.2.5
°²³]
F ¬O¤@Ó field ¥B
char(
F) =
p 0, «h¹ï¥ô·N
a,
b F,
§Ú̦³
(
a +
b)
pn =
apn +
bpn and (
a -
b)
pn =
apn -
bpn,
n .
µý ©ú.
§ÚÌ¥ý¥Î induction ÃÒ©ú
(
a +
b)
pn =
apn +
bpn. º¥ý¦Ò¼
n = 1 ªº±¡ªp. §ÚÌ¥ýÀˬd (
a +
b)
2 ¬°¦ó? ¥Ñ©ó
(
a +
b)
2 =
a2 +
a . b +
b . a +
b2, §Q¥Î
F ¬O¤@Ó field ª¾
a . b =
b . a,
¦]¦¹§Ú̱o
(
a +
b)
2 =
a2 + 2(
a . b) +
b2. ¦A¦¸±j½Õ³o¸Ì
2(
a . b)
¬O
(
a . b) + (
a . b) ¦Ó¤£¬O
2
. (
a . b).
©Ò¥HÄ Äò¤U¥h§ÚÌ¥i¥H§Q¥ÎÃþ¦ü¤G¶µ¦¡©w²z±o
(
a +
b)
p =
ap +
p(
ap - 1 . b) +
... +
(
ai . bp - i) +
... +
bp.
¥Ñ©ó
char(
F) =
p, ¹ï¥ô·N
F,
¦Û¤v³s¥[¦Û¤v
p ¦¸µ¥©ó 0 (§Y
p = 0). ¤j®a³£ª¾¹D·í
p ¬O½è¼Æ¥B·í
i = 1,...,
p - 1 ®É,
¬O
p ªº¿¼Æ,
¬Gª¾¦¹®É
(
ai . bp - i) = 0. ¦]¦¹§ÚÌ¥i±o
(a + b)p = ap + bp. |
(9.2) |
²§Q¥ÎÂk¯Ç°²³]
(a + b)pn - 1 = apn - 1 + bpn - 1, |
(9.3) |
¬G§Q¥Î¦¡¤l (
9.2)
©M (
9.3) §Ú̪¾
(a + b)pn = (a + b)pn - 1 = (apn - 1 + bpn - 1)p = apn + bpn. |
|
±µ¤U¨ÓÃÒ©ú
(a - b)pn = apn - bpn. º¥ýª`·N·í
char(F) = 2 ®É,
¹ï¥ô·N
F §Ú̦³
+ = 2 = 0, ¬Gª¾
= - . ¦]¦¹¦b p = 2 ®É§Ú̦۵M¦³
(a - b)pn = (a + b)pn = apn + bpn = apn - bpn.
¦Ó·í
p ¬O odd prime number ®É, ¥Ñ©ó¹ï¥ô·N
¬Ò¦³
(-
)
pn = -
(Corollary
5.2.4), §Ú̱o
(
a -
b)
pn =
a + (-
b)
=
apn + (-
b)
pn =
apn -
bpn.
Lemma 9.2.5 ¤]¥i¥H±À¼s¨ì F[x] ¤Wªº¹Bºâ. ª`·N F[x] ¤Wªº
polynomial ªº«Y¼Æ³£¦b F ¤¤, ¦Ó¥B F[x]
¤Wªº¥[ªk¨Ì©w¸q¬O±N¦P¦¸¶µªº«Y¼Æ³£¥[°_¨Ó. ¦]¦¹Y
char(F) = p ®É,
¹ï¥ô·Nªº
f (x) = anxn + ... + a0 F[x] §Ú̳£¦³
¦]¦¹§Q¥ÎÃþ¦ü Lemma 9.2.5 ªºÃÒ©ú§Ú̦³¥H¤Uªº©Ê½è:
Lemma 9.2.6
°²³]
F ¬O¤@Ó field ¥B
char(
F) =
p 0, «h¹ï¥ô·N
f (
x) =
amxm +
... +
a0 F[
x], §Ú̦³
(
f (
x))
pn =
ampnxmpn +
... +
a0pn,
n .
¯S§O·í
a F ®É, §Ú̦³
(
x -
a)
pn =
xpn -
apn,
n .
¤U¤@¶: ½u©Ê¥N¼ÆªºÀ³¥Î
¤W¤@¶: ªì¯Å Field ªº©Ê½è
«e¤@¶: Field ªº°ò¥»©Ê½è
Administrator
2005-06-18