We completely characterise the computational complexity of the list homomorphism problem for graphs in combinatorial and algebraic terms: for every graph H the problem is either N...
In a variety of emerging applications one needs to decide whether a graph G matches another Gp, i.e., whether G has a topological structure similar to that of Gp. The traditional ...
By use of elementary geometric arguments we prove the existence of a special integral solution of a certain system of linear equations. The existence of such a solution yields the...
For digraphs D and H, a mapping f : V (D)→V (H) is a homomorphism of D to H if uv ∈ A(D) implies f(u)f(v) ∈ A(H). If, moreover, each vertex u ∈ V (D) is associated with co...