Square-free graphs are multiplicative

Square-free graphs are multiplicative

Graph homomorphism is an ubiquitous notion in graph theory with a variety of applications, and a first step to understanding more general constraints given by relational structures, see e.g. the monograph of Hell and Nešetřil [5]. We write μ : G→ H if μ is a homomorphism from the graph G to H, or simply G → H if such a homomorphism exists. For example, a graph G is k-colorable iff it has a homo...

Square-free perfect graphs

Square-free colorings of graphs

Let G be a graph and let c be a coloring of its edges. If the sequence of colors along a walk of G is of the form a1, . . . , an, a1, . . . , an, the walk is called a square walk. We say that the coloring c is squarefree if any open walk is not a square and call the minimum number of colors needed so that G has a square-free coloring a walk Thue number and denote it by πw(G). This concept is a ...

Coloring square-free Berge graphs

We consider the class of Berge graphs that do not contain a chordless cycle of length four. We present a purely graph-theoretical algorithm that produces an optimal coloring in polynomial time for every graph in that

Algorithms for Square-3PC(., .)-Free Berge Graphs

We consider the class of graphs containing no odd hole, no odd antihole, and no configuration consisting of three paths between two nodes such that any two of the paths induce a hole, and at least two of the paths are of length 2. This class generalizes clawfree Berge graphs and square-free Berge graphs. We give a combinatorial algorithm of complexity O(n) to find a clique of maximum weight in ...