scholarly journals ON CUTS IN ULTRAPRODUCTS OF LINEAR ORDERS II

2018 ◽  
Vol 83 (1) ◽  
pp. 29-39
Author(s):  
MOHAMMAD GOLSHANI ◽  
SAHARON SHELAH

AbstractWe continue our study of the class ${\cal C}\left( D \right)$, where D is a uniform ultrafilter on a cardinal κ and ${\cal C}\left( D \right)$ is the class of all pairs $\left( {{\theta _1},{\theta _2}} \right)$, where $\left( {{\theta _1},{\theta _2}} \right)$ is the cofinality of a cut in ${J^\kappa }/D$ and J is some ${\left( {{\theta _1} + {\theta _2}} \right)^ + }$-saturated dense linear order. We give a combinatorial characterization of the class ${\cal C}\left( D \right)$. We also show that if $\left( {{\theta _1},{\theta _2}} \right) \in {\cal C}\left( D \right)$ and D is ${\aleph _1}$-complete or ${\theta _1} + {\theta _2} > {2^\kappa }$, then ${\theta _1} = {\theta _2}$.

2017 ◽  
Vol 82 (2) ◽  
pp. 648-671 ◽  
Author(s):  
GABRIEL CONANT

AbstractWe use axioms of abstract ternary relations to define the notion of a free amalgamation theory. These form a subclass of first-order theories, without the strict order property, encompassing many prominent examples of countable structures in relational languages, in which the class of algebraically closed substructures is closed under free amalgamation. We show that any free amalgamation theory has elimination of hyperimaginaries and weak elimination of imaginaries. With this result, we use several families of well-known homogeneous structures to give new examples of rosy theories. We then prove that, for free amalgamation theories, simplicity coincides with NTP2 and, assuming modularity, with NSOP3 as well. We also show that any simple free amalgamation theory is 1-based. Finally, we prove a combinatorial characterization of simplicity for Fraïssé limits with free amalgamation, which provides new context for the fact that the generic Kn-free graphs are SOP3, while the higher arity generic $K_n^r$-free r-hypergraphs are simple.


2017 ◽  
Vol 82 (2) ◽  
pp. 453-473 ◽  
Author(s):  
RICHARD RAST ◽  
DAVENDER SINGH SAHOTA

AbstractGiven a countable o-minimal theory T, we characterize the Borel complexity of isomorphism for countable models of T up to two model-theoretic invariants. If T admits a nonsimple type, then it is shown to be Borel complete by embedding the isomorphism problem for linear orders into the isomorphism problem for models of T. This is done by constructing models with specific linear orders in the tail of the Archimedean ladder of a suitable nonsimple type.If the theory admits no nonsimple types, then we use Mayer’s characterization of isomorphism for such theories to compute invariants for countable models. If the theory is small, then the invariant is real-valued, and therefore its isomorphism relation is smooth. If not, the invariant corresponds to a countable set of reals, and therefore the isomorphism relation is Borel equivalent to F2.Combining these two results, we conclude that $\left( {{\rm{Mod}}\left( T \right), \cong } \right)$ is either maximally complicated or maximally uncomplicated (subject to completely general model-theoretic lower bounds based on the number of types and the number of countable models).


1989 ◽  
Vol 54 (3) ◽  
pp. 865-874 ◽  
Author(s):  
Alain Louveau

AbstractWe prove two results about the embeddability relation between Borel linear orders: For η a countable ordinal, let 2η (resp. 2< η) be the set of sequences of zeros and ones of length η (resp. < η), equipped with the lexicographic ordering. Given a Borel linear order X and a countable ordinal ξ, we prove the following two facts.(a) Either X can be embedded (in a (X, ξ) way) in 2ωξ or 2ωξ + 1 continuously embeds in X.(b) Either X can embedded (in a (X, ξ) way) in 2<ωξ or 2ωξ continuously embeds in X. These results extend previous work of Harrington, Shelah and Marker.


2016 ◽  
Vol 37 (6) ◽  
pp. 1997-2016 ◽  
Author(s):  
YINGQING XIAO ◽  
FEI YANG

In this paper, we study the dynamics of the family of rational maps with two parameters $$\begin{eqnarray}f_{a,b}(z)=z^{n}+\frac{a^{2}}{z^{n}-b}+\frac{a^{2}}{b},\end{eqnarray}$$ where $n\geq 2$ and $a,b\in \mathbb{C}^{\ast }$. We give a characterization of the topological properties of the Julia set and the Fatou set of $f_{a,b}$ according to the dynamical behavior of the orbits of the free critical points.


2018 ◽  
Vol 33 (24) ◽  
pp. 4165-4172 ◽  
Author(s):  
Deepak Kumar ◽  
Prasanta Mandal ◽  
Anil Singh ◽  
Charu Pant ◽  
Sudesh Sharma

Abstract


2013 ◽  
Vol 28 (13) ◽  
pp. 1740-1746 ◽  
Author(s):  
Nishant Gupta ◽  
Rajendra Singh ◽  
Fan Wu ◽  
Jagdish Narayan ◽  
Colin McMillen ◽  
...  

Abstract


2015 ◽  
Vol 30 (9) ◽  
pp. 1473-1484 ◽  
Author(s):  
Clarissa A. Yablinsky ◽  
Ram Devanathan ◽  
Janne Pakarinen ◽  
Jian Gan ◽  
Daniel Severin ◽  
...  

Abstract


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