More on the complexity of cover graphs
In response to [3] and [4] we prove that the recognition of cover graphs of finite posets is an NP-hard problem.
More set-theory around the weak Freese–Nation property
We introduce a very weak version of the square principle which may hold even under failure of the generalized continuum hypothesis. Under this weak square principle, we give a new characterization (Theorem 10) of partial orderings with κ-Freese-Nation property (see below for the definition). The characterization is not a ZFC theorem: assuming Chang’s Conjecture for , we can find a counter-example to the characterization (Theorem 12). We then show that, in the model obtained by adding Cohen reals,...
Multiabbildungen und Anordnungen der Mengen
Natural generalization of some lattice theory concepts to partially ordered sets
ndependence of axioms for biordered sets.
Near lattices
New results for EP matrices in indefinite inner product spaces
In this paper we study -EP matrices, as a generalization of EP-matrices in indefinite inner product spaces, with respect to indefinite matrix product. We give some properties concerning EP and -EP matrices and find connection between them. Also, we present some results for reverse order law for Moore-Penrose inverse in indefinite setting. Finally, we deal with the star partial ordering and improve some results given in the “EP matrices in indefinite inner product spaces” (2012), by relaxing some...
Nonexistence of nonmolecular generic sets.
Normal Fitting Classes and the Lockett Ordering.
Note on canonizing ordering theorems for Hales Jewett structures
Note on Demi-Topological Functors.
Note on orthocomplemented posets II.
Note on quasi-orders, partial orders and orders
On a characterization of the lattice of -ideals of an ordered set
On a construction of amalgamation I
On a local property of the unoriented graph of a modular multilattice
On a power of cyclically ordered sets
On a property of partially ordered sets.
On A System Of All Maximal Chains (Antichains) Of A Graph
On an axiom concerning the theory of “interval orders”.