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Inner functions in the unit ball of Cn
Authors:Walter Rudin
Institution:University of Wisconsin-Madison, Madison, Wisconsin 53706 USA
Abstract:Let B be the open unit ball of Cn, n > 1. Let I (for “inner”) be the set of all u ? H °(B) that have ¦u¦ = 1 a.e. on the boundary S of B. Aleksandrov proved recently that there exist nonconstant u ? I. This paper strengthens his basic theorem and provides further information about I and the algebra Q generated by I. Let XY be the finite linear span of products xy, x ? X, y ? Y, and let ¦X¦ be the norm closure, in L = L(S), of X. Some results: set I is dense in the unit ball of H(B) in the compact-open topology. On S, Q?Q is weak1-dense in L, ¦Q? does not contain H, C(S) ?¦Q?H¦ ≠ ¦H?H¦ ≠ L. (When n = 1, ¦Q¦ = Hand ¦Q?Q¦ = L.) Every unimodular ? ? L is a pointwise limit a.e. of products uv?, u ? I, ν ? I. The zeros of every ? ? 0 in the ball algebra (but not of every H-function) can be matched by those of some u ? I, as can any finite number of derivatives at 0 if ∥?∥ < 1. However, ?u cannot be bounded in B if u ? I is non-constant.
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