Let us denote by the class of all finite simple graphs. A property of graphs
is any nonempty proper isomorphism closed subclass of .
Let
be properties of graphs. A graph is vertex
-colorable( has property
) if the vertex set of can be partitioned into sets
such that the subgraph of induced by belongs to ; .
In the case
we write
and we say that
is -colorable (partitionable).
Let us denote by the class of all edgeless graphs. The classical graph coloring problems deals with so-called proper coloring where
so that a graph is -colorable if and only if
. We consider as the generalizations of the proper coloring only such vertex
-colorings where the properties
preserve the above mentioned requirements i.e. they are closed to induced subgraphs and disjoint union of graphs. Such properties of graphs are called induced-hereditary and additive. The set of all additive induced-hereditary properties will be denoted by
.
Let
, an edge
-decomposition of
a graph is the decomposition
of its edge set
satisfying that for each
the induced
subgraph has property . A property
is defined as the set of all graphs having a
-decomposition.
If
we simply write
instead of
.
Reducible and decomposable properties of graphs express a natural generalization of vertex and edge -colorable graphs. The detailed notation, basic results and many examples of induced-hereditary properties may be found in [1] and [2].
An additive induced-hereditary property
is said to be reducible (decomposable) if there exist additive induced-hereditary properties and such that
; otherwise the property is irreducible (indecomposable). In our talk we will present a survey of open problems on reducible and decomposable properties of graphs and present a lot of examples of concrete properties.