G-Compactness and Groups

Lascar described E_KP as a composition of E_L and the topological closure of EL. We generalize this result to some other pairs of equivalence relations. Motivated by an attempt to construct a new example of a non-G-compact theory, we consider the following example. Assume G is a group definable in a structure M. We define a structure M_0 consisting of M and X as two sorts, where X is an affine copy of G and in M_0 we have the structure of M and the action of G on X. We prove that the Lascar group of M_0 is a semi-direct product of the Lascar group of M and G/G_L. We discuss the relationship between G-compactness of M and M_0. This example may yield new examples of non-G-compact theories.Comment: 18 page

ON ORDERED MINIMAL STRUCTURES

We investigate minimal rst-order structures and consider interpretability and denability of orderings on them. We also prove the minimality of their canonical substructures

ℳ-rank and meager groups

Assume p* is a meager type in a superstable theory T. We investigate definability properties of p*-closure. We prove that if T has $<2^{ℵ_0}$ countable models then the multiplicity rank ℳ of every type p is finite. We improve Saffe's conjecture

Czy logika formalna ma sens?

Does formal logic make sense?This text is a commentary on the book Logika i argumentacja. Praktyczny kurs krytycznego myślenia Logic and Argumentation. A Practical Course In Critical Thinking by Professor Andrzej Kisielewicz. Prof. Kisielewicz argues there, among other things, that formal symbolic logic is inadequate to explain practical rational reasoning. This commentary defends formal logic in this respect. In particular, Prof. Kisielewicz proposes in his book a definition of practical logical inference. According to him, a conclusion follows from a given set of premises if there is no situation, where the premises hold, while the conclusion fails. In this commentary it is pointed out that this is a well-known notion of semantic inference in formal logic. It is also well-known that semantic and syntactic inference in logic are equivalent, i.e. equally strong.&nbsp;Does formal logic make sense?This text is a commentary on the book Logika i argumentacja. Praktyczny kurs krytycznego myślenia Logic and Argumentation. A Practical Course In Critical Thinking by Professor Andrzej Kisielewicz. Prof. Kisielewicz argues there, among other things, that formal symbolic logic is inadequate to explain practical rational reasoning. This commentary defends formal logic in this respect. In particular, Prof. Kisielewicz proposes in his book a definition of practical logical inference. According to him, a conclusion follows from a given set of premises if there is no situation, where the premises hold, while the conclusion fails. In this commentary it is pointed out that this is a well-known notion of semantic inference in formal logic. It is also well-known that semantic and syntactic inference in logic are equivalent, i.e. equally strong

ℳ-rank and meager types

Assume T is superstable and small. Using the multiplicity rank ℳ we find locally modular types in the same manner as U-rank considerations yield regular types. We define local versions of ℳ-rank, which also yield meager types