Isomorphisms of Royden Type Algebras Over
Teresa Radice, Eero Saksman, Gabriella Zecca (2009)
Bollettino dell'Unione Matematica Italiana
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Let and be the unit circle and the unit disc in the plane and let us denote by the algebra of the complex-valued continuous functions on which are traces of functions in the Sobolev class . On we define the following norm where is the harmonic extension of to . We prove that every isomorphism of the functional algebra is a quasitsymmetric change of variables on .