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Interval decomposition lattices are balanced

Foldes S., Radeleczki S.

Demonstratio Mathematica

2016

Vol. 49, nr 3

271--281

Intervals in binary or n-ary relations or other discrete structures generalize the concept of an interval in a linearly ordered set. They are defined abstractly as closed sets of a closure system on a set, satisfying certain axioms. Join-irreducible partitions into intervals are characterized in the lattice of all interval decompositions. This result is used to show that the lattice of interval decompositions is balanced, and the case when this lattice is distributive is also characterised.

Σ-genomorphism of algebraic structures

Emanovský P.

Demonstratio Mathematica

2003

Vol. 36, nr 4

785--792

For an algebraic structure A = (A, F, R) of type τ and a set Σ of open formulas of the first order language L(τ), the concept of Σ-closed subset of A was introduced in [3]. The set C Σ(A) of all Σ-closed subsets of A forms a complete lattice whose properties were studied in [3], [4] and [5]. Algebraic structures A, B of type τ are called CΣ-isomorphic (or Σ-isomorphic in [3]) if the lattices CΣ(A) and CΣ(B) are isomorphic. The CΣ-isomorphisms are investigated for so-called Σ-separable algebraic structures in [3]. The study of the Σ-isomorphisms of algebraic structures is continued in this paper. We introduce the concepts of Σ-genomorphism and Σ-isogenomorphism of algebraic structures and we formulate a sufficient condition under which two structures are isomorphic. We show that for Σ-separable structures the condition is also necessary. Further, we introduce the concepts of Σ-morphism, congruential E -morphism and congruence induced by a congruential Σ-morphism. We also prove Theorem on Σ-genomorphism and Theorem on Σ-morphism.