: u, W4 i: |# J0 _& N4 \* r教材是algebra micheal artin的) E5 X9 ^5 j3 P! p/ i
在他讲群的时候引入了S3 对称群 : _3 H, N( @& ~' [9 A) n q' j. r9 `take the cyclic permutation(1 2 3),the transposition(1 2) 5 ^8 M) }& z6 N0 p* a0 D0 A3 g
then obtain the rules:% H9 `/ t( `8 ^% ^7 c: h# @
x^3=1 y^2=1 yx=(x^2)y , B- v- m6 m* ~) y7 MI wanna know why yx=(x^2)y ! n, u7 S+ G# kthx..: F# q |$ k( i* v7 W
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another quesition# l5 [% ^2 c! j2 l- z( T
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 d1 e' K6 H/ u+ y5 K
分数表示为什么要单独拿出来说一下? 这不是abelian group么。