证设A∈P B∈P×mn 1)ⅢABm1=∑∑1∑ aikbk j=1i=1k=1 ∑∑∑|aik l。丨b,: i=1k=1 ∑∑∑|aik|°|bk; k=1i=1j=1 ∑C|ak||bD k=1L=1证 m l l n A P B P   设  ,    = = = = n j m i l k AB m ai kbkj 1 1 1 1) || || | | 1  = = =  • n j m i l k ai k bkj 1 1 1 | | | | ( | | | |) 1 1 1    = = = = • l k m i n j ai k bkj    = = = = • l k m i n j aik bk j 1 1 1 | | | |