If f is a non-zero analytic function on the open annulus A= {z in ; 1<|z|<2}, how can I prove that there exists an integer m such that for all r . 1<r<2, 1/ i _{|z|=r} f '(z)/f(z) dz =m ?
Thanks.
A proof of the 'argument principle theorem' is here...
http://www.joensuu.fi/matematiikka/k...plex/luku3.pdf
Kind regards