A note on extremal decompositions of covariances

A Note on Extremal Combinatorics of Cyclic Split Systems

It is shown that every cyclic split system S defined on an n-set with #S > 2kn− (2k+1 2 ) for some k ≤ n−1 2 always contains a subset of k+1 pairwise incompatible splits provided one has min(k, n−(2k+1)) ≤ 3. In addition, some related old and new conjectures are also discussed.

A note on edge-decompositions of planar graphs

We give conditions for different classes of planar graphs to be decomposable into paths of length 3.

A Note on Semilattice Decompositions of Completely Π-regular Semigroups

We study completely π-regular semigroups admitting a decomposition into a semilattice of σn-simple semigroups, and describe them in terms of properties of their idempotents. In the general case, semigroups admitting a decomposition into a semilattice of σn-simple semigroups were characterized by M. Ćirić and S. Bogdanović in [3] (see Theorem 1 below), in terms of paths of length n in the graph ...

A note on the uniqueness of global static decompositions

We discuss when static Killing vector fields are standard, that is, leading to a global orthogonal splitting of the spacetime. We prove that such an orthogonal splitting is unique whenever the natural space is compact. This is carried out by proving that many notable spacelike submanifolds must be contained in an orthogonal slice. Possible obstructions to the global splitting are also considere...

A note on decompositions of transitive tournaments II