Let $0<t_0<1$  fixed number , $ n_0$ integer $ \geq 2$ fixed  and let  $\forall 0<u<1, f(u)= \displaystyle \frac{(1-u)^n \log(1-u)}{(1-ut_0)^{n+1}} $.

Let $0<u_0<1 $ be given.  I'm looking a good upper bound ( wich is an explicit  function in $u_0,t_0, n_0$) to $ |f^{(n_0)}(u_0)|$ ( derivative $n_0$ ieme) . 

I suppose that by Cauchy formula, and choosing the good radius one can have the good upper bound. but i dont know how to do it. Any help?