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A Neighborhood Condition for Fractional ID-[A, B]-Factor-Critical Graphs

Sizhong Zhou, Fan Yang, Zhiren Sun (2016)

Discussiones Mathematicae Graph Theory

Let G be a graph of order n, and let a and b be two integers with 1 ≤ a ≤ b. Let h : E(G) → [0, 1] be a function. If a ≤ ∑e∋x h(e) ≤ b holds for any x ∈ V (G), then we call G[Fh] a fractional [a, b]-factor of G with indicator function h, where Fh = {e ∈ E(G) : h(e) > 0}. A graph G is fractional independent-set-deletable [a, b]-factor-critical (in short, fractional ID-[a, b]- factor-critical) if G − I has a fractional [a, b]-factor for every independent set I of G. In this paper, it is proved...

A new and stronger central sets theorem

Dibyendu De, Neil Hindman, Dona Strauss (2008)

Fundamenta Mathematicae

Furstenberg's original Central Sets Theorem applied to central subsets of ℕ and finitely many specified sequences in ℤ. In this form it was already strong enough to derive some very strong combinatorial consequences, such as the fact that a central subset of ℕ contains solutions to all partition regular systems of homogeneous equations. Subsequently the Central Sets Theorem was extended to apply to arbitrary semigroups and countably many specified sequences. In this paper we derive a new version...

A new approach to chordal graphs

Ladislav Nebeský (2007)

Czechoslovak Mathematical Journal

By a chordal graph is meant a graph with no induced cycle of length 4 . By a ternary system is meant an ordered pair ( W , T ) , where W is a finite nonempty set, and T W × W × W . Ternary systems satisfying certain axioms (A1)–(A5) are studied in this paper; note that these axioms can be formulated in a language of the first-order logic. For every finite nonempty set W , a bijective mapping from the set of all connected chordal graphs G with V ( G ) = W onto the set of all ternary systems ( W , T ) satisfying the axioms (A1)–(A5) is...

A New Characterization of Unichord-Free Graphs

Terry A. McKee (2015)

Discussiones Mathematicae Graph Theory

Unichord-free graphs are defined as having no cycle with a unique chord. They have appeared in several papers recently and are also characterized by minimal separators always inducing edgeless subgraphs (in contrast to characterizing chordal graphs by minimal separators always inducing complete subgraphs). A new characterization of unichord-free graphs corresponds to a suitable reformulation of the standard simplicial vertex characterization of chordal graphs.

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