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Uniquely partitionable planar graphs with respect to properties having a forbidden tree

100%
Bucko J., Ivančo J.
Discussiones Mathematicae Graph Theory
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1999
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tom 19
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nr 1
71-78
EN
Let 𝓟₁, 𝓟₂ be graph properties. A vertex (𝓟₁,𝓟₂)-partition of a graph G is a partition {V₁,V₂} of V(G) such that for i = 1,2 the induced subgraph $G[V_i]$ has the property $𝓟_i$. A property ℜ = 𝓟₁∘𝓟₂ is defined to be the set of all graphs having a vertex (𝓟₁,𝓟₂)-partition. A graph G ∈ 𝓟₁∘𝓟₂ is said to be uniquely (𝓟₁,𝓟₂)-partitionable if G has exactly one vertex (𝓟₁,𝓟₂)-partition. In this note, we show the existence of uniquely partitionable planar graphs with respect to hereditary additive properties having a forbidden tree.
2
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On infinite uniquely partitionable graphs and graph properties of finite character

100%
Bucko J., Mihók P.
Discussiones Mathematicae Graph Theory
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2009
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tom 29
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nr 2
241-251
EN
A graph property is any nonempty isomorphism-closed class of simple (finite or infinite) graphs. A graph property 𝓟 is of finite character if a graph G has a property 𝓟 if and only if every finite induced subgraph of G has a property 𝓟. Let 𝓟₁,𝓟₂,...,𝓟ₙ be graph properties of finite character, a graph G is said to be (uniquely) (𝓟₁, 𝓟₂, ...,𝓟ₙ)-partitionable if there is an (exactly one) partition {V₁, V₂, ..., Vₙ} of V(G) such that $G[V_i] ∈ 𝓟_i$ for i = 1,2,...,n. Let us denote by ℜ = 𝓟₁ ∘ 𝓟₂ ∘ ... ∘ 𝓟ₙ the class of all (𝓟₁,𝓟₂,...,𝓟ₙ)-partitionable graphs. A property ℜ = 𝓟₁ ∘ 𝓟₂ ∘ ... ∘ 𝓟ₙ, n ≥ 2 is said to be reducible. We prove that any reducible additive graph property ℜ of finite character has a uniquely (𝓟₁, 𝓟₂, ...,𝓟ₙ)-partitionable countable generating graph. We also prove that for a reducible additive hereditary graph property ℜ of finite character there exists a weakly universal countable graph if and only if each property $𝓟_i$ has a weakly universal graph.
3
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On uniquely partitionable relational structures and object systems

100%
Bucko J., Mihók P.
Discussiones Mathematicae Graph Theory
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2006
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tom 26
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nr 2
281-289
EN
We introduce object systems as a common generalization of graphs, hypergraphs, digraphs and relational structures. Let C be a concrete category, a simple object system over C is an ordered pair S = (V,E), where E = {A₁,A₂,...,Aₘ} is a finite set of the objects of C, such that the ground-set $V(A_i)$ of each object $A_i ∈ E$ is a finite set with at least two elements and $V ⊇ ⋃_{i=1}^m V(A_i)$. To generalize the results on graph colourings to simple object systems we define, analogously as for graphs, that an additive induced-hereditary property of simple object systems over a category C is any class of systems closed under isomorphism, induced-subsystems and disjoint union of systems, respectively. We present a survey of recent results and conditions for object systems to be uniquely partitionable into subsystems of given properties.
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Criteria for of the existence of uniquely partitionable graphs with respect to additive induced-hereditary properties

81%
Broere I., Bucko J., Mihók P.
Discussiones Mathematicae Graph Theory
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2002
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tom 22
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nr 1
31-37
EN
Let 𝓟₁,𝓟₂,...,𝓟ₙ be graph properties, a graph G is said to be uniquely (𝓟₁,𝓟₂, ...,𝓟ₙ)-partitionable if there is exactly one (unordered) partition {V₁,V₂,...,Vₙ} of V(G) such that $G[V_i] ∈ 𝓟_i$ for i = 1,2,...,n. We prove that for additive and induced-hereditary properties uniquely (𝓟₁,𝓟₂,...,𝓟ₙ)-partitionable graphs exist if and only if $𝓟_i$ and $𝓟_j$ are either coprime or equal irreducible properties of graphs for every i ≠ j, i,j ∈ {1,2,...,n}.
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Uniquely partitionable graphs

81%
Bucko J., Frick M., Mihók P., Vasky R.
Discussiones Mathematicae Graph Theory
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1997
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tom 17
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nr 1
103-113
EN
Let 𝓟₁,...,𝓟ₙ be properties of graphs. A (𝓟₁,...,𝓟ₙ)-partition of a graph G is a partition of the vertex set V(G) into subsets V₁, ...,Vₙ such that the subgraph $G[V_i]$ induced by $V_i$ has property $𝓟_i$; i = 1,...,n. A graph G is said to be uniquely (𝓟₁, ...,𝓟ₙ)-partitionable if G has exactly one (𝓟₁,...,𝓟ₙ)-partition. A property 𝓟 is called hereditary if every subgraph of every graph with property 𝓟 also has property 𝓟. If every graph that is a disjoint union of two graphs that have property 𝓟 also has property 𝓟, then we say that 𝓟 is additive. A property 𝓟 is called degenerate if there exists a bipartite graph that does not have property 𝓟. In this paper, we prove that if 𝓟₁,..., 𝓟ₙ are degenerate, additive, hereditary properties of graphs, then there exists a uniquely (𝓟₁,...,𝓟ₙ)-partitionable graph.
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Note on partitions of planar graphs

81%
Broere I., Wilson B., Bucko J.
Discussiones Mathematicae Graph Theory
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2005
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tom 25
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nr 1-2
211-215
EN
Chartrand and Kronk in 1969 showed that there are planar graphs whose vertices cannot be partitioned into two parts inducing acyclic subgraphs. In this note we show that the same is true even in the case when one of the partition classes is required to be triangle-free only.
7
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A note on maximal common subgraphs of the Dirac's family of graphs

81%
Bucko J., Mihók P., Saclé J.-F., Woźniak M.
Discussiones Mathematicae Graph Theory
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2005
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tom 25
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nr 3
385-390
EN
Let 𝓕 ⁿ be a given set of unlabeled simple graphs of order n. A maximal common subgraph of the graphs of the set 𝓕 ⁿ is a common subgraph F of order n of each member of 𝓕 ⁿ, that is not properly contained in any larger common subgraph of each member of 𝓕 ⁿ. By well-known Dirac's Theorem, the Dirac's family 𝓓𝓕 ⁿ of the graphs of order n and minimum degree δ ≥ [n/2] has a maximal common subgraph containing Cₙ. In this note we study the problem of determining all maximal common subgraphs of the Dirac's family $𝓓 𝓕 ^{2n}$ for n ≥ 2.
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