For graphs there are only four types of hereditary Ramsey classes

On Hereditary Helly Classes of Graphs

In graph theory, the Helly property has been applied to families of sets, such as cliques, disks, bicliques, and neighbourhoods, leading to the classes of clique-Helly, disk-Helly, biclique-Helly, neighbourhood-Helly graphs, respectively. A natural question is to determine for which graphs the corresponding Helly property holds, for every induced subgraph. This leads to the corresponding classe...

Role colouring graphs in hereditary classes

We study the computational complexity of computing role colourings of graphs in hereditary classes. We are interested in describing the family of hereditary classes on which a role colouring with k colours can be computed in polynomial time. In particular, we wish to describe the boundary between the “hard” and “easy” classes. The notion of a boundary class has been introduced by Alekseev in or...

When There Are Only Minorities

Intergroup relation perspectives stem from research in Western contexts with clear distinctions between the dominant and nondominant groups. In South Africa, with at least 13 different cultural groups and 11 official languages, no group is dominant in all life spheres. We examine the relationship between identity and in-/out-group orientation across Black-Zulu, Coloured (mixed racial ancestry),...

There Are No Particles, There Are Only Fields

Quantum foundations are still unsettled, with mixed effects on science and society. By now it should be possible to obtain consensus on at least one issue: Are the fundamental constituents fields or particles? As this paper shows, experiment and theory imply that unbounded fields, not bounded particles, are fundamental. This is especially clear for relativistic systems, implying that it's also ...

Finite Presentation of Homogeneous Graphs , Posets and Ramsey Classes