Spanning sets of powers on wild Jordan curves
โ Scribed by Jacob Korevaar; Pia Pfluger
- Publisher
- Elsevier Science
- Year
- 1974
- Weight
- 526 KB
- Volume
- 77
- Category
- Article
- ISSN
- 1385-7258
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โฆ Synopsis
SIIMMARY
Let y be a Jordan curve in the z-plane which contains the origin in its interior . Every continuous function on y is uniformly approximable by polynomials in z and 1/z (Walsh) . If y is rectifiable, all powers zn are required to obtain a spanning set for C(y), but it has been observed (Warmer) that for nonrectifiable y, the power zo=1 is superfluous . The authors obtain a formula for the distance in C(y) between a given power of a and the closed span of all but a finite number of the other powers (Theorem 2) . This formula leads to various geometric conditions on y under which one can omit a given (finite) number of powers z++, and still have a spanning set left (Section 5) . The basic tool in the paper is a Walsh type theorem with side conditions (Section 2) .
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