On the characterization of complex rational approximations
Daniel E. Wulbert · Illinois Journal of Mathematics · 1980
An example is constructed showing that best uniform approximation (local or global) from $R_{n}^{m}(\mathbf{c})$ can not be characterized by linearization techniques or by alternation properties of the error function. A class of local best approximations are characterized, and used to demonstrate approximation properties of $R_{n}^{m}(\mathbf{c})$.