D F/DI B B E′ E 于f(z)dz=0 f(z)dz=o AEBBEA A AaF B BFA6 D C C 1 A A' B' B D 1 F E E' F' ( ) d 0 ( ) d 0 ' ' ' ' ' ' = =   AEBB E A A A A F B BFA f z z f z z