Boundary-analytic disk algebra with doubled character space
ID: boundary-analytic-disk-algebra-with-doubled-character-space
Let consist of continuous functions on the closed unit disk whose boundary values extend to a member of the disk algebra. The extension is unique by the maximum modulus principle; the extension map is a surjective unital algebra homomorphism of norm at most one. Its kernel is the ideal of functions vanishing on the boundary. A character vanishing on factors through , so it is for some closed-disk point . For a character not vanishing on , choose with . The rule extends to a character of all continuous functions on the disk: multiplicativity follows from . It is therefore evaluation at an interior point, since its value at is nonzero. These two closed-disk families agree exactly on their boundaries. Their glued compact space maps continuously and bijectively to the Hausdorff character space of an algebra, giving the stated homeomorphism. The algebra is closed because uniform convergence of boundary data gives uniform convergence of their analytic extensions.
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