Fractal Intersections and Products via Algorithmic Dimension

Algorithmic fractal dimensions quantify the algorithmic information density of individual points and may be defined in terms of Kolmogorov complexity. This work uses these dimensions to bound the classical Hausdorff and packing dimensions of intersections and Cartesian products of fractals in Euclidean spaces. This approach shows that two prominent, fundamental results about the dimension of Borel or analytic sets also hold for arbitrary sets.

BOUNDNESS OF INTERSECTION NUMBERS FOR ACTIONS BY TWO-DIMENSIONAL BIHOLOMORPHISMS

We say that a group G of local (maybe formal) biholomorphisms satisfies the uniform intersection property if the intersection multiplicity $(\phi (V), W)$ takes only finitely many values as a function of G for any choice of analytic sets V and W of complementary dimension. In dimension $2$ we show that G satisfies the uniform intersection property if and only if it is finitely determined – that is, if there exists a natural number k such that different elements of G have different Taylor expansions of degree k at the origin. We also prove that G is finitely determined if and only if the action of G on the space of germs of analytic curves has discrete orbits.

Value distribution of derivatives in polynomial dynamics

For every $m\in \mathbb {N}$ , we establish the equidistribution of the sequence of the averaged pullbacks of a Dirac measure at any given value in $\mathbb {C}\setminus \{0\}$ under the $m$ th order derivatives of the iterates of a polynomials $f\in \mathbb {C}[z]$ of degree $d>1$ towards the harmonic measure of the filled-in Julia set of f with pole at $\infty $ . We also establish non-archimedean and arithmetic counterparts using the potential theory on the Berkovich projective line and the adelic equidistribution theory over a number field k for a sequence of effective divisors on $\mathbb {P}^1(\overline {k})$ having small diagonals and small heights. We show a similar result on the equidistribution of the analytic sets where the derivative of each iterate of a Hénon-type polynomial automorphism of $\mathbb {C}^2$ has a given eigenvalue.

Nikolai Nikolaevich Luzin at the crossroads of the dramatic events of the European history of the first half of the 20th century

Nikolai Nikolaevich Luzin’s life (1883–1950) and work of this outstanding Russian mathematician, member of the USSR Academy of Sciences and foreign member of the Polish Academy of Arts and Sciences, coincides with a very difficult period in Russian history: two World Wars, the 1917 revolution in Russia, the coming to power of the Bolsheviks, the civil war of 1917–1922, and finally, the construction of a new type of state, the Union of Soviet Socialist Republics. This included collectivization in the agriculture and industrialization of the industry, accompanied by the mass terror that without exception affected all the strata of the Soviet society. Against the background of these dramatic events took place the proces of formation and flourishing of Luzin the scientist, the creator of one of the leading mathematical schools of the 20th century, the Moscow school of function theory, which became one of the cornerstones in the foundation of the Soviet mathematical school. Luzin’s work could be divided into two periods: the first one comprises the problems regarding the metric theory of functions, culminating in his famous dissertation Integral and Trigonometric Series (1915), and the second one that is mainly devoted to the development of problems arising from the theory of analytic sets. The underlying idea of Luzin’s research was the problem of the structure of the arithmetic continuum, which became the super task of his work. The destiny favored the master: the complex turns of history in which he was involved did not prevent, and sometimes even favored the successful development of his research. And even the catastrophe that broke out over him in 1936 – “the case of Academician Luzin” – ended successfully for him.