Word reversing is a combinatorial operation on words that detects pairs of equivalent words in monoids that admit a presentation of a certain form. Here we give conditions for this...
A simple characterization of the 3, 4, or 5-colorable Eulerian triangulations of the projective plane is given. Key words: Projective plane, triangulation, coloring, Eulerian grap...
A tree function (TF) t on a ÿnite set X is a real function on the set of the pairs of elements of X satisfying the four-point condition: for all distinct x; y; z; w ∈ X; t(xy)+...
We investigate the following question: “Given an intersecting multi-hypergraph on n points, what fraction of edges must be covered by any of the best 2 points?” (Here “best...
Abstract. Given a partially ordered set P = (X; P ), a function F which assigns to each x 2 X a set F (x) so that x y in P if and only if F (x) F (y) is called an inclusion represe...
Stefan Felsner, Peter C. Fishburn, William T. Trot...