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The Douady-Earle extension of quasihomographies

Ken-Ichi Sakan, Józef Zając (1996)

Banach Center Publications

Quasihomography is a useful notion to represent a sense-preserving automorphism of the unit circle T which admits a quasiconformal extension to the unit disc. For K ≥ 1 let A T ( K ) denote the family of all K-quasihomographies of T. With any f A T ( K ) we associate the Douady-Earle extension E f and give an explicit and asymptotically sharp estimate of the L norm of the complex dilatation of E f .

Uniformly convex functions II

Wancang Ma, David Minda (1993)

Annales Polonici Mathematici

Recently, A. W. Goodman introduced the class UCV of normalized uniformly convex functions. We present some sharp coefficient bounds for functions f(z) = z + a₂z² + a₃z³ + ... ∈ UCV and their inverses f - 1 ( w ) = w + d w ² + d w ³ + . . . . The series expansion for f - 1 ( w ) converges when | w | < ϱ f , where 0 < ϱ f depends on f. The sharp bounds on | a n | and all extremal functions were known for n = 2 and 3; the extremal functions consist of a certain function k ∈ UCV and its rotations. We obtain the sharp bounds on | a n | and all extremal functions for n = 4, 5,...

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