例如乘法结合律 ● ∑aX)∑bX)C∑c) ∑(∑ab1)X)C∠cX) =0计+j=k 1=0 ∑(∑(∑ab)c)X o k+l=m i+j=k ∑(∑abc)X m=0 i+j+l=m ∑a)∑(∑bc)X) i=0 k=0 i+l=k10 例如乘法结合律 ( )( )( ) 0 0 0     =  =  = l l l j j j i i ai X b X c X ( ( ) )( ) 0 0     =  = + = = l l l k k i j k ai bj X c X     = + = + = = 0 ( ( ) ) m m l i j k i j k l m a b c X    = + + = = 0 ( ) m m l i j l m ai bj c X     = + =  = = 0 0 ( )( ( ) ) k k l j l k j i i ai X b c X