本帖最后由 bomboom 于 2013-3-10 14:39 编辑 5 W0 l7 N, @, a# U _; U 0 `# O. n8 h, s/ ^. W教材是algebra micheal artin的) P O3 B2 W( l+ M- Q9 _) }# y7 Q; r
在他讲群的时候引入了S3 对称群* q- Z( d. U$ k
take the cyclic permutation(1 2 3),the transposition(1 2) % e+ M C, W" Q7 O) _' ^* x+ {! e
then obtain the rules:' f6 ~3 g+ t8 |# s( b/ T
x^3=1 y^2=1 yx=(x^2)y3 z. Z8 _+ b2 }6 s/ D6 r
I wanna know why yx=(x^2)y0 f+ L$ S4 w9 f, `
thx.. ; C1 Y# S4 V; ? 6 t1 l# U* A0 }+ c" Q! S/ a1 f; M
another quesition# b! O9 w+ @: O, \7 g
Fraction notation b/a is not advisable unless the law of composition is commutative, because it is not clear whether the fraction stands for b(a^-1) or (a^-1)b 7 ^- \- Z8 S( \7 m! q- }分数表示为什么要单独拿出来说一下? 这不是abelian group么。