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Some questions of definability
Lechner, Jiří ; Stanovský, David (advisor) ; Kepka, Tomáš (referee)
We focus on first-order definability in the quasiordered class of finite digraphs ordered by embeddability. At first we will prove definability of each digraph up to size three. We will need to add to the quasiorder structure some digraphs as constants, so we try to find the needed set of constants as small as possible with small digraph as well. Gradually we make instruments that we can use to express the inner structure of each digraphs in the language of embeddability. At the end we investigate definability in the closely related lattice of universal classes of digraphs. We show that the set of finitely generated and also the set of finitely axiomatizable universal classes are definable subsets of the lattice.
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Kombinatorika matematických struktur
Paták, Pavel
The combinatorics of a first order mathematical structure is the class of all formulas valid in all in it definable structures. This notion was first introduced by Krajíček in [6]. In the present work we try to characterize and compare the combinatorics of several different prominent structures (reals, complex number, dense linear order, . . . ). We also study the question of algorithmical complexity, i.e. the question how hard it is to check whether a given formula lies in the combinatorics of a given structure. We prove that this question is corecursively enumeratively complete and therefore algorithmicaly undecidable in the case of models of complete theories without strict order property (SOP) and in the case of pseudofinite structures.
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Some questions of definability
Lechner, Jiří ; Stanovský, David (advisor) ; Kepka, Tomáš (referee)
We focus on first-order definability in the quasiordered class of finite digraphs ordered by embeddability. At first we will prove definability of each digraph up to size three. We will need to add to the quasiorder structure some digraphs as constants, so we try to find the needed set of constants as small as possible with small digraph as well. Gradually we make instruments that we can use to express the inner structure of each digraphs in the language of embeddability. At the end we investigate definability in the closely related lattice of universal classes of digraphs. We show that the set of finitely generated and also the set of finitely axiomatizable universal classes are definable subsets of the lattice.
|
|
|
Kombinatorika matematických struktur
Paták, Pavel
The combinatorics of a first order mathematical structure is the class of all formulas valid in all in it definable structures. This notion was first introduced by Krajíček in [6]. In the present work we try to characterize and compare the combinatorics of several different prominent structures (reals, complex number, dense linear order, . . . ). We also study the question of algorithmical complexity, i.e. the question how hard it is to check whether a given formula lies in the combinatorics of a given structure. We prove that this question is corecursively enumeratively complete and therefore algorithmicaly undecidable in the case of models of complete theories without strict order property (SOP) and in the case of pseudofinite structures.
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