International Journal of Mathematics and Mathematical Sciences
Volume 5 (1982), Issue 2, Pages 351-356
doi:10.1155/S0161171282000337
On the differentiability of T(r,f)
Douglas W. Townsend
Department of Mathematical Sciences, Indiana University-Purdue University at Fort Wayne, Fort Wayne 46805, Indiana, USA
Abstract
It is well known that T(r,f) is differentiable at least for r>r0. We show that, in fact, T(r,f) is differentiable for all but at most one value of r, and if T(r,f) fails to have a derivative for some value of r, then f is a constant times a quotient of finite Blaschke products.