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Frankl’s conjecture for large semimodular and planar semimodular lattices

Gábor Czédli, E. Tamás Schmidt (2008)

Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica

A lattice L is said to satisfy (the lattice theoretic version of) Frankl’s conjecture if there is a join-irreducible element f L such that at most half of the elements x of L satisfy f x . Frankl’s conjecture, also called as union-closed sets conjecture, is well-known in combinatorics, and it is equivalent to the statement that every finite lattice satisfies Frankl’s conjecture. Let m denote the number of nonzero join-irreducible elements of L . It is well-known that L consists of at most 2 m elements....

Free -groups and free products of -groups

Dao Rong Tong (1994)

Commentationes Mathematicae Universitatis Carolinae

In this paper we have given the construction of free -groups generated by a po-group and the construction of free products in any sub-product class 𝒰 of i -groups. We have proved that the 𝒰 -free products satisfy the weak subalgebra property.

Free trees and the optimal bound in Wehrung's theorem

Pavel Růžička (2008)

Fundamenta Mathematicae

We prove that there is a distributive (∨,0,1)-semilattice of size ℵ₂ such that there is no weakly distributive (∨,0)-homomorphism from C o n c A to with 1 in its range, for any algebra A with either a congruence-compatible structure of a (∨,1)-semi-lattice or a congruence-compatible structure of a lattice. In particular, is not isomorphic to the (∨,0)-semilattice of compact congruences of any lattice. This improves Wehrung’s solution of Dilworth’s Congruence Lattice Problem, by giving the best cardinality...

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