URA 751 au CNRS & UFR de Mathématiques, Université de Lille I, F--59655 Villeneuve d'Ascq, France ; URA 751 au CNRS & UFR de Mathématiques, Université de Lille I, F--59655 Villeneuve d'Ascq, France
Abstract:
Suppose that is left invertible in for all , where is an open subset of the complex plane. Then an operator-valued function is a left resolvent of in if and only if has an extension , the resolvent of which is a dilation of of a particular form. Generalized resolvents exist on every open set , with included in the regular domain of . This implies a formula for the maximal radius of regularity of in terms of the spectral radius of its generalized inverses. A solution to an open problem raised by J. Zemánek is obtained.