Christina Zarb

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A degree monotone path in a graph G is a path P such that the sequence of degrees of the vertices in the order in which they appear on P is monotonic. The length (number of vertices) of the longest degree monotone path in G is denoted by mp(G). This parameter, inspired by the well-known ErdősSzekeres theorem, has been studied by the authors in two earlier(More)
A constrained colouring or, more specifically, an (α, β)-colouring of a hypergraph H, is an assignment of colours to its vertices such that no edge of H contains less than α or more than β vertices with different colours. This notion, introduced by Bujtás and Tuza, generalises both classical hypergraph colourings and more general Voloshin colourings of(More)
Let σ be a partition of the positive integer r. A σ-hypergraph H = H(n, r, q|σ) is an r-uniform hypergraph on nq vertices which are partitioned into n classes V1, V2, . . . , Vn each containing q vertices. An r-subset K of vertices is an edge of the hypergraph if the partition of r formed by the non-zero cardinalities |K ∩ Vi|, 1 ≤ i ≤ n, is σ. In earlier(More)
A path v1, v2, . . . , vm in a graph G is degree-monotone if deg(v1) ≤ deg(v2) ≤ · · · ≤ deg(vm) where deg(vi) is the degree of vi in G. Longest degree-monotone paths have been studied in several recent papers. Here we consider the Ramsey type problem for degree monotone paths. Denote by Mk(m) the minimum number M such that for all n ≥ M , in any k-edge(More)
We define and study a special type of hypergraph. A σ-hypergraph H = H(n, r, q | σ), where σ is a partition of r, is an r-uniform hypergraph having nq vertices partitioned into n classes of q vertices each. If the classes are denoted by V1, V2,...,Vn, then a subset K of V (H) of size r is an edge if the partition of r formed by the non-zero cardinalities |(More)
We consider vertex colourings of r-uniform hypergraphs H in the classical sense, that is such that no edge has all its vertices given the same colour, and (2, 2)-colourings of H in which the vertices in any edge are given exactly two colours. This is a special case of constrained colourings introduced by Bujtas and Tuza which, in turn, is a generalization(More)
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