Properties of the automorphism group and a probabilistic construction of a class of countable labeled structures

AbstractFor a class of countably infinite ultrahomogeneous structures that generalize edge-colored graphs we provide a probabilistic construction. Also, we give fairly general criteria for the automorphism group of such structures to have the small index property and strong uncountable cofinality, thus generalizing some results of Solecki, Rosendal, and several other authors

Hereditarily indecomposable continua as generic mathematical structures

We characterize the pseudo-arc as well as P-adic pseudo-solenoids (for a set of primes P) as generic structures, arising from a natural game in which two players alternate in building an inverse sequence of surjections. The second player wins if the limit of this sequence is homeomorphic to a concrete (fixed in advance) space, called generic whenever the second player has a winning strategy. For this aim, we develop a new approximate Fra\"iss\'e theory, in order to realize the above-mentioned objects (the pseudo-arc and the pseudo-solenoids) as Fra\"iss\'e limits. Our framework extends the discrete Fra\"iss\'e theory, both classical and projective, and is also suitable for working directly with continuous maps on metrizable compacta. We show, in particular, that, when playing with continuous surjections between non-degenerate Peano continua, the pseudo-arc is always generic. The universal pseudo-solenoid appears to be generic over all surjections between circle-like continua.Comment: 64 pages, 2 figures, comments are welcom

Topological properties of Wazewski dendrite groups

Homeomorphism groups of generalized Wa\.zewski dendrites act on the infinite countable set of branch points of the dendrite and thus have a nice Polish topology. In this paper, we study them in the light of this Polish topology. The group of the universal Wa\.zewski dendrite $D_\infty$ is more characteristic than the others because it is the unique one with a dense conjugacy class. For this group $G_\infty$, we show some of its topological properties like existence of a comeager conjugacy class, the Steinhaus property, automatic continuity and the small index subgroup property. Moreover, we identify the universal minimal flow of $G_\infty$. This allows us to prove that point-stabilizers in $G_\infty$ are amenable and to describe the universal Furstenberg boundary of $G_\infty$.Comment: Slight modifications about the expositio