∮f()k=0,| F 2 AEBBEAA B ∮f(z)k=0 AAFB'BFA E ∮f(z)+∮f(z)d+∫f(x)+∫f(z)l AA A'A +∫f(z)l+∫f(z)dz=0 B'B BB ∮f(z)/+∮f(z)d=0.→f(x)=∮f(z)( ) 0, AEBB EA A f z dz    = ( ) 0. AA F B BFA f z dz     = 1 ( ) ( ) ( ) ( ) ( ) ( ) 0. c c AA A A B B BB f z dz f z dz f z dz f z dz f z dz f z dz −     + + + + + =       1 ( ) ( ) 0. c c f z dz f z dz −  + =   上两式相加得 1 ( ) ( ) . c c  =   f z dz f z dz c1 c2 A E F B A  B  F  E  D