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Two results on a partial ordering of finite sequences

Martin Klazar (1993)

Commentationes Mathematicae Universitatis Carolinae

In the first part of the paper we are concerned about finite sequences (over arbitrary symbols) u for which E x ( u , n ) = O ( n ) . The function E x ( u , n ) measures the maximum length of finite sequences over n symbols which contain no subsequence of the type u . It follows from the result of Hart and Sharir that the containment a b a b a u is a (minimal) obstacle to E x ( u , n ) = O ( n ) . We show by means of a construction due to Sharir and Wiernik that there is another obstacle to the linear growth. In the second part of the paper we investigate whether...

Two variants of the size Ramsey number

Andrzej Kurek, Andrzej Ruciński (2005)

Discussiones Mathematicae Graph Theory

Given a graph H and an integer r ≥ 2, let G → (H,r) denote the Ramsey property of a graph G, that is, every r-coloring of the edges of G results in a monochromatic copy of H. Further, let m ( G ) = m a x F G | E ( F ) | / | V ( F ) | and define the Ramsey density m i n f ( H , r ) as the infimum of m(G) over all graphs G such that G → (H,r). In the first part of this paper we show that when H is a complete graph Kₖ on k vertices, then m i n f ( H , r ) = ( R - 1 ) / 2 , where R = R(k;r) is the classical Ramsey number. As a corollary we derive a new proof of the result credited to Chvatál...

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