| Contents | 6 |
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| List of Contributors | 8 |
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| Introduction | 10 |
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| Acknowledgements | 15 |
| 1 The youth of Andrei Nikolaevich and Fourier series | 16 |
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| 1.1 Convergence and divergence of Fourier series | 16 |
| 1.2 Harmonic conjugates and Fourier series | 18 |
| 1.3 Fourier series, integration and probability | 19 |
| 1.4 The descendants of the articles of young Kolmogorov | 21 |
| Appendix: Two other aspects of Kolmogorov’s results concerning harmonic conjugates | 24 |
| I The A-integral of Kolmogorov | 24 |
| II On the weak (1,1) type of the harmonic conjugate | 25 |
| References | 25 |
| 2 Kolmogorov’s contribution to intuitionistic logic | 28 |
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| 2.1 The first paper (1925). Formalization of intuitionistic logic | 28 |
| 2.2 Classical and intuitionistic mathematics | 35 |
| 2.3 Refinements of Kolmogorov’s result | 38 |
| 2.4 A calculus of problems | 39 |
| 2.5 Some recent developments | 41 |
| 2.6 A calculus of problems for classical logic? | 43 |
| References | 45 |
| 3 Some aspects of the probabilistic work | 50 |
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| 3.1 Introduction | 50 |
| 3.2 The axiomatization of probability calculus | 51 |
| 3.3 Limit theorems and series of independent random variables | 55 |
| 3.4 Processes in continuous time | 60 |
| References | 73 |
| 4 Infinite-dimensional Kolmogorov equations | 76 |
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| 4.1 Introduction and setting of the problem | 76 |
| 4.2 The Ornstein-Uhlenbeck semigroup | 87 |
| 4.3 Regular nonlinearities | 94 |
| 4.4 Some Kolmogorov equations arising in the applications | 95 |
| References | 102 |
| 5 From Kolmogorov’s theorem on empirical distribution to number theory | 106 |
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| 5.1 Introduction | 106 |
| 5.2 New estimates for uniform order statistics | 109 |
| 5.3 Number theory applications | 112 |
| Acknowledgement | 115 |
| References | 115 |
| 6 Kolmogorov’s e-entropy and the problem of statistical estimation | 118 |
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| 6.1 Overview of the problem: parametric and non- parametric statistics | 118 |
| 6.2 Notations and definitions | 120 |
| 6.3 The Kullback-Leibler distance and the maximum likelihood estimator | 123 |
| 6.4 The entropy of a partition and Fano’s inequality | 124 |
| 6.5 The lower bound for the minimax risk | 130 |
| 6.6 Consistency of the estimation | 137 |
| 6.7 The estimator of the minimal distance | 138 |
| 6.8 Using entropy to estimate a density | 141 |
| Conclusion | 144 |
| References | 144 |
| 7 Kolmogorov and topology | 148 |
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| 7.1 Prelude | 148 |
| 7.2 The main topological results of A. N. Kolmogorov | 151 |
| 7.3 A topological idea of Kolmogorov | 156 |
| References | 157 |
| 8 Geometry and approximation theory in A. N. Kolmogorov’s works | 160 |
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| 8.1 Geometric motives in Kolmogorov’s works | 160 |
| 8.2 Kolmogorov’s works on the approximation theory | 176 |
| References | 184 |
| 9 Kolmogorov and population dynamics | 186 |
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| 9.1 Introduction | 186 |
| 9.2 From Volterra equations to Gause equations | 187 |
| 9.3 The Kolmogorov equations | 188 |
| 9.4 Technical aspects | 190 |
| 9.5 The impact | 191 |
| References | 193 |
| 10 Resonances and small divisors | 196 |
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| 10.1 A periodic world | 196 |
| 10.2 Kepler, Newton. . . | 200 |
| 10.3 An almost periodic world | 203 |
| 10.4 Lagrange and Laplace: the almost periodic world | 203 |
| 10.5 Poincar´e and chaos | 207 |
| 10.6 A “toy model” of the theory of perturbations | 208 |
| 10.7 Solution to the stability problem “in the toy model” | 214 |
| 10.8 Are the irrational diophantine numbers rare or abundant? | 216 |
| 10.9 A statement of the theorem of Kolmogorov- Arnold- Moser | 217 |
| 10.10 Is the KAM theorem useful in our solar system? | 219 |
| References | 221 |
| 11 The KAM Theorem | 224 |
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| 11.1 The solar system | 225 |
| 11.2 The forced pendulum | 233 |
| 11.3 Summary of Hamiltonian mechanics | 236 |
| 11.4 A precise statement of Kolmogorov’s theorem | 241 |
| 11.5 Strategy of the proof | 242 |
| References | 246 |
| 12 From Kolmogorov’s work on entropy of dynamical systems to non- uniformly hyperbolic dynamics | 248 |
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| 12.1 General dynamical systems | 248 |
| 12.2 Kolmogorov’s paper on entropy | 249 |
| 12.3 The notion of hyperbolicity | 251 |
| 12.4 Lorenz system | 252 |
| 12.5 Hyperbolicity in one-dimensional systems | 253 |
| 12.6 Two-dimensional systems | 255 |
| 12.7 Conservative systems | 256 |
| 12.8 Conclusion | 258 |
| References | 258 |
| 13 From Hilbert’s 13th Problem to the theory of neural networks: constructive aspects of Kolmogorov’s Superposition Theorem | 262 |
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| 13.1 Hilbert’s 13th problem | 262 |
| 13.2 Kolmogorov’s Superposition Theorem | 264 |
| 13.3 Computability of Sprecher’s function | 266 |
| 13.4 A computable Kolmogorov Superposition Theorem | 274 |
| 13.5 Aspects of dimension | 277 |
| 13.6 Aspects of constructivity | 279 |
| 13.7 Applications to feedforward neural networks | 281 |
| 13.8 Conclusion | 284 |
| 13.9 Acknowledgement | 285 |
| References | 285 |
| 14 Kolmogorov complexity | 290 |
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| 14.1 Algorithms | 290 |
| 14.2 Descriptions and sizes | 294 |
| 14.3 Gödel’s theorem | 297 |
| 14.4 Definition of randomness | 301 |
| Acknowledgement | 307 |
| References | 307 |
| 15 Algorithmic chaos and the incompressibility method | 310 |
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| 15.1 Introduction | 310 |
| 15.2 Kolmogorov complexity | 313 |
| 15.3 Algorithmic chaos theory | 318 |
| Acknowledgement | 325 |
| References | 325 |