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38
Generation theory for semigroups of holomorphic mappings in Banach spaces
 Abstr. Appl. Anal
, 1996
"... Abstract. We study nonlinear semigroups ofholomorphic mappings in Banach spaces and their infinitesimal generators. Using resolvents, we characterize, in particular, bounded holomorphic generators on bounded convex domains and obtain an analog ofthe Hille exponential formula. We then apply our resul ..."
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Cited by 22 (15 self)
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Abstract. We study nonlinear semigroups ofholomorphic mappings in Banach spaces and their infinitesimal generators. Using resolvents, we characterize, in particular, bounded holomorphic generators on bounded convex domains and obtain an analog ofthe Hille exponential formula. We then apply our results to the null point theory ofsemiplus complete vector fields. We study the structure ofnull point sets and the spectral characteristics of null points, as well as their existence and uniqueness. A global version of the implicit function theorem and a discussion of some open problems are also included.
Asymptotically nonexpansive mappings in uniformly convex hyperbolic spaces
, 2008
"... This paper provides a fixed point theorem for asymptotically nonexpansive mappings in uniformly convex hyperbolic spaces as well as new effective results on the KrasnoselskiMann iterations of such mappings. The latter were found using methods from logic and the paper continues a case study in the g ..."
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Cited by 17 (10 self)
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This paper provides a fixed point theorem for asymptotically nonexpansive mappings in uniformly convex hyperbolic spaces as well as new effective results on the KrasnoselskiMann iterations of such mappings. The latter were found using methods from logic and the paper continues a case study in the general program of extracting effective data from primafacie ineffective proofs in the fixed point theory of such mappings.
Proof Interpretations and the Computational Content of Proofs. Draft of book in preparation
, 2007
"... This survey reports on some recent developments in the project of applying proof theory to proofs in core mathematics. The historical roots, however, go back to Hilbert’s central theme in the foundations of mathematics which can be paraphrased by the following question ..."
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Cited by 16 (2 self)
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This survey reports on some recent developments in the project of applying proof theory to proofs in core mathematics. The historical roots, however, go back to Hilbert’s central theme in the foundations of mathematics which can be paraphrased by the following question
Fixed point theorems in CAT(0) spaces and Rtrees
 Fixed Point Theory and Applications
"... We show that ifU is a bounded open set in a complete CAT(0) spaceX, and if f:U → X is nonexpansive, then f always has a fixed point if there exists p ∈U such that x / ∈ [p, f (x)) for all x ∈ ∂U. It is also shown that if K is a geodesically bounded closed convex subset of a complete Rtree with int( ..."
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Cited by 10 (0 self)
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We show that ifU is a bounded open set in a complete CAT(0) spaceX, and if f:U → X is nonexpansive, then f always has a fixed point if there exists p ∈U such that x / ∈ [p, f (x)) for all x ∈ ∂U. It is also shown that if K is a geodesically bounded closed convex subset of a complete Rtree with int(K) = ∅, and if f: K → X is a continuous mapping for which x / ∈ [p, f (x)) for some p ∈ int(K) and all x ∈ ∂K, then f has a fixed point. It is also noted that a geodesically bounded complete Rtree has the fixed point property for continuous mappings. These latter results are used to obtain variants of the classical fixed edge theorem in graph theory. 1.
Nonexpansive iterations in uniformly convex Whyperbolic spaces
, 2008
"... We propose the class of uniformly convex Whyperbolic spaces with monotone modulus of uniform convexity (UCWhyperbolic spaces for short) as an appropriate setting for the study of nonexpansive iterations. UCWhyperbolic spaces are a natural generalization both of uniformly convex normed spaces and ..."
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Cited by 5 (0 self)
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We propose the class of uniformly convex Whyperbolic spaces with monotone modulus of uniform convexity (UCWhyperbolic spaces for short) as an appropriate setting for the study of nonexpansive iterations. UCWhyperbolic spaces are a natural generalization both of uniformly convex normed spaces and CAT(0)spaces. Furthermore, we apply proof mining techniques to get effective rates of asymptotic regularity for Ishikawa iterations of nonexpansive selfmappings of closed convex subsets in UCWhyperbolic spaces. These effective results are new even for uniformly convex Banach spaces.
Effective metastability of Halpern iterates in CAT(0) spaces
"... This paper provides an effective uniform rate of metastability (in the sense of Tao) on the strong convergence of Halpern iterations of nonexpansive mappings in CAT(0) spaces. The extraction of this rate from an ineffective proof due to Saejung is an instance of the general proof mining program whic ..."
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Cited by 5 (2 self)
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This paper provides an effective uniform rate of metastability (in the sense of Tao) on the strong convergence of Halpern iterations of nonexpansive mappings in CAT(0) spaces. The extraction of this rate from an ineffective proof due to Saejung is an instance of the general proof mining program which uses tools from mathematical logic to uncover hidden computational content from proofs. This methodology is applied here for the first time to a proof that uses Banach limits and hence makes a substantial reference to the axiom of choice.