Beyond First Order Logic: from Number of Structures to Structure of Numbers Part Ii

The paper studies the history and recent developments in non-elementary model theory focusing in the framework of abstract elementary classes. We discuss the role of syntax and semantics and the motivation to generalize first order model theory to non-elementary frameworks and illuminate the study with concrete examples of classes of models. This second part continues to study the question of catecoricity transfer and counting the number of structures of certain cardinality. We discuss more thoroughly the role of countable models, search for a non-elementary counterpart for the concept of completeness and present two examples: One example answers a question asked by David Kueker and the other investigates models of Peano Arihmetic and the relation of an elementary end-extension in the terms of an abstract elementary class. Beyond First Order Logic: From number of structures to structure of numbers Part I studied the basic concepts in non-elementary model theory, such as syntax and semantics, the languages Lλκ and the notion of a complete theory in first order logic (i.e. in the language Lωω), which determines an elementary class of structures. Classes of structures which cannot be axiomatized as the models of a first-order theory, but might have some other ’logical’ unifying attribute, are called non-elementary. MSC(2010): Primary: 65F05; Secondary: 46L05, 11Y50.