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pro vyhledávání: '"Andréka, H."'
The function $p_{xy}$ that interchanges two logical variables $x,y$ in formulas is hard to describe in the following sense. Let $F$ denote the Lindenbaum-Tarski formula-algebra of a finite-variable first order logic, endowed with $p_{xy}$ as a unary
Externí odkaz:
http://arxiv.org/abs/2409.04088
A logic family is a bunch of logics that belong together in some way. First-order logic is one of the examples. Logics organized into a structure occurs in abstract model theory, institution theory and in algebraic logic. Logic families play a role i
Externí odkaz:
http://arxiv.org/abs/2311.00759
This note contains some material promised in our earlier papers on submodel preservation and the guarded fragment, along with some information on the current status of the problems mentioned in these papers. Section 1 contains an early example of fai
Externí odkaz:
http://arxiv.org/abs/2303.13222
Two first-order logic theories are definitionally equivalent if and only if there is a bijection between their model classes that preserves isomorphisms and ultraproducts (Theorem 2). This is a variant of a prior theorem of van Benthem and Pearce. In
Externí odkaz:
http://arxiv.org/abs/2211.14232
Autor:
Andréka, H., Németi, I.
We prove that the two-variable fragment of first-order logic has the weak Beth definability property. This makes the two-variable fragment a natural logic separating the weak and the strong Beth properties since it does not have the strong Beth defin
Externí odkaz:
http://arxiv.org/abs/2010.00901
Autor:
Andréka, H., Németi, I.
We prove that persistently finite algebras are not created by completions of algebras, in any ordered discriminator variety. A persistently finite algebra is one without infinite simple extensions. We prove that finite measurable relation algebras ar
Externí odkaz:
http://arxiv.org/abs/1810.04569
A series of nonrepresentable relation algebras is constructed from groups. We use them to prove that there are continuum many subvarieties between the variety of representable relation algebras and the variety of coset relation algebras. We present o
Externí odkaz:
http://arxiv.org/abs/1809.05473
Autor:
Givant, S., Andréka, H.
A relation algebra is called measurable when its identity is the sum of measurable atoms, and an atom is called measurable if its square is the sum of functional elements. In this paper we show that atomic measurable relation algebras have rather str
Externí odkaz:
http://arxiv.org/abs/1808.03924
Autor:
Andréka, H., Givant, S.
A measurable relation algebra is a relation algebra in which the identity element is a sum of atoms that can be measured in the sense that the "size" of each such atom can be defined in an intuitive and reasonable way (within the framework of the fir
Externí odkaz:
http://arxiv.org/abs/1804.00279
Autor:
Andréka, H., Németi, I.
We exhibit two relation algebra atom structures such that they are elementarily equivalent but their term algebras are not. This answers Problem 14.19 in the book Hirsch, R. and Hodkinson, I., "Relation Algebras by Games", North-Holland, 2002.
Externí odkaz:
http://arxiv.org/abs/1803.11038