≤EC∑a;k|∑|b k=1i=1k=1 ∑∑|akD(∑∑|bkD i=1k=1 =‖lm‖!B‖ 2)‖AB‖m2=(∑∑|∑ aikbk;)2 j=1i=1k=1( | | | |) 1 1 1 1    = = = =  • l k m i n j kj l k ai k b ( | |) ( | |) 1 1 1 1   = = = = = • m i l k n j kj l k ai k b 1 1 = || A||m • || B||m 2 1 1 1 1 2 2) || || ( | | ) 2    = = = = n j m i l k A B m aikbk j