Graph homomorphisms are used to study good characterizations for coloring problems (Trans. Amer. Math. Soc. 384 (1996), 1281–1297; Discrete Math. 22 (1978), 287–300). Particularly, the following concept arises in this context: A pair of graphs (A, B) is called a homomorphism duality if for any graph G either there exists a homomorphism σ : A→ G or there exists a homomorphism τ : G → B but not b...

A reflexive graph is a simple undirected graph where a loop has been added at each vertex. If G and H are reflexive graphs and U ⊆ V (H), then a vertex map f : U → V (G) is called nonexpansive if for every two vertices x, y ∈ U , the distance between f(x) and f(y) in G is at most that between x and y in H . A reflexive graph G is said to have the extension property (EP) if for every reflexive g...

We define a (chaotic) deterministic variant of random multiplicative cascade models of turbulence. It preserves the hierarchical tree structure , thanks to the addition of infinitesimal noise. The zero-noise limit can be handled by Perron-Frobenius theory, just as the zero-diffusivity limit for the fast dynamo problem. Random multiplicative models do not possess Kolmogorov 1941 (K41) scaling be...

For any two graphs F and G, let hom(F,G) denote the number of homomorphisms F → G, that is, adjacency preserving maps V (F ) → V (G) (graphs may have loops but no multiple edges). We characterize Institute of Mathematics, Eötvös Loránd University, Budapest, Hungary. Email: [email protected]. Research sponsored by OTKA Grant No. 67867. CWI and University of Amsterdam, Amsterdam, The Netherlands....

Let G be a finite group. We show that the Bass Nil-groups NKn(RG), n ∈ Z, are generated from the p-subgroups of G by induction, certain twistings maps depending on elements in the centralizers of the psubgroups, and the Verschiebung homomorphisms. As a consequence, the groups NKn(RG) are generated by induction from elementary subgroups. For NK0(ZG) we get an improved estimate of the torsion exp...

We deene a (chaotic) deterministic variant of random multiplicative cascade models of turbulence. It preserves the hierarchical tree structure , thanks to the addition of innnitesimal noise. The zero-noise limit can be handled by Perron-Frobenius theory, just as the zero-diiusivity limit for the fast dynamo problem. Random multiplicative models do not possess Kolmogorov 1941 (K41) scaling becau...

Behavioural equivalences of labelled transition systems are characterized in terms of homomorphic transformations. This permits relying on algebraic techniques for proving systems properties and reduces equivalence checking of two systems to studying the relationships among the elements of their structures. Di6erent algebraic characterizations of bisimulation-based equivalences in terms of part...

We study morphisms of the generalized quantum logic tripotents in JBW $$^*$$ -triples and von Neumann algebras. Especially, we establish a generalization celebrated Dye’s theorem on orthoisomorphisms between lattices to this new context. show existence one-to-one correspondence following maps: (1) posets preserving reflection $$u\rightarrow - u$$ (2) maps triples that preserve are real linear s...