1. CMB 2015 (vol 59 pp. 3)
||The Contraction Principle for Multivalued Mappings on a Modular Metric Space with a Graph|
We study the existence of fixed points for contraction multivalued
mappings in modular metric spaces endowed with a graph. The
notion of a modular metric on an arbitrary set and the corresponding
modular spaces, generalizing classical modulars over linear spaces
like Orlicz spaces, were recently introduced. This paper can
be seen as a generalization of Nadler's and Edelstein's fixed
point theorems to modular metric spaces endowed with a graph.
Keywords:fixed point theory, modular metric spaces, multivalued contraction mapping, connected digraph.
Categories:47H09, 46B20, 47H10, 47E10
2. CMB 2013 (vol 57 pp. 141)
||Size, Order, and Connected Domination|
We give a sharp upper bound on the size of a
triangle-free graph of a given order and connected domination. Our
bound, apart from
strengthening an old classical theorem of Mantel and of
TurÃ¡n , improves on a theorem of Sanchis.
Further, as corollaries, we settle a long standing
conjecture of Graffiti on the leaf number and local independence for
triangle-free graphs and answer a question of Griggs, Kleitman and
Shastri on a lower bound of the leaf number in
Keywords:size, connected domination, local independence number, leaf number
3. CMB 2012 (vol 56 pp. 860)
||On Countable Dense and $n$-homogeneity|
We prove that a connected, countable dense homogeneous space is
$n$-homogeneous for every $n$, and strongly 2-homogeneous provided it
is locally connected. We also present an example of a connected and
countable dense homogeneous space which is not strongly
2-homogeneous. This answers Problem 136 of Watson in the Open Problems
in Topology Book in the negative.
Keywords:countable dense homogeneous, connected, $n$-homogeneous, strongly $n$-homogeneous, counterexample
Categories:54H15, 54C10, 54F05
4. CMB 2011 (vol 54 pp. 244)
||Homogeneous Suslinian Continua|
A continuum is said to be Suslinian if it does not
contain uncountably many
mutually exclusive non-degenerate subcontinua. Fitzpatrick and
Lelek have shown that a metric Suslinian continuum $X$ has the
property that the set of points at which $X$ is connected im
kleinen is dense in $X$. We extend their result to Hausdorff Suslinian continua
and obtain a number of corollaries. In particular, we prove that a homogeneous,
non-degenerate, Suslinian continuum is a simple closed curve and that each separable,
non-degenerate, homogenous, Suslinian continuum is metrizable.
Keywords:connected im kleinen, homogeneity, Suslinian, locally connected continuum
Categories:54F15, 54C05, 54F05, 54F50
5. CMB 2009 (vol 52 pp. 416)
||Hamiltonian Properties of Generalized Halin Graphs |
A Halin graph is a graph $H=T\cup C$, where $T$ is a tree with no
vertex of degree two, and $C$ is a cycle connecting the end-vertices
of $T$ in the cyclic order determined by a plane embedding of $T$.
In this paper, we define classes of generalized Halin graphs, called
$k$-Halin graphs, and investigate their Hamiltonian properties.
Keywords:$k$-Halin graph, Hamiltonian, Hamiltonian connected, traceable
6. CMB 2005 (vol 48 pp. 195)
||On Suslinian Continua |
A continuum is said to be Suslinian if it does not contain uncountably
many mutually exclusive nondegenerate subcontinua. We prove that
Suslinian continua are perfectly normal and rim-metrizable. Locally
connected Suslinian continua have weight at most $\omega_1$ and under
appropriate set-theoretic conditions are metrizable. Non-separable
locally connected Suslinian continua are rim-finite on some open set.
Keywords:Suslinian continuum, Souslin line, locally connected, rim-metrizable,, perfectly normal, rim-finite
Categories:54F15, 54D15, 54F50