45,213 research outputs found
An Isomorphism Theorem for Graphs
In the 1970’s, L. Lovász proved that two graphs G and H are isomorphic if and only if for every graph X , the number of homomorphisms from X → G equals the number of homomorphisms from X → H . He used this result to deduce cancellation properties of the direct product of graphs. We develop a result analogous to Lovász’s theorem, but in the class of graphs without loops and with weak homomorphisms. We apply it prove a general cancellation property for the strong product of graphs
A Lexicographic Product Cancellation Property for Digraphs
There are four prominent product graphs in graph theory: Cartesian, strong, direct, and lexicographic. Of these four product graphs, the lexicographic product graph is the least studied. Lexicographic products are not commutative but still have some interesting properties. This paper begins with basic definitions of graph theory, including the definition of a graph, that are needed to understand theorems and proofs that come later. The paper then discusses the lexicographic product of digraphs, denoted , for some digraphs and . The paper concludes by proving a cancellation property for the lexicographic product of digraphs , , , and : if and , then . It also proves additional cancellation properties for lexicographic product digraphs and the author hopes the final result will provide further insight into tournaments
Geometry of infinitely presented small cancellation groups, Rapid Decay and quasi-homomorphisms
We study the geometry of infinitely presented groups satisfying the small
cancelation condition C'(1/8), and define a standard decomposition (called the
criss-cross decomposition) for the elements of such groups. We use it to prove
the Rapid Decay property for groups with the stronger small cancelation
property C'(1/10). As a consequence, the Metric Approximation Property holds
for the reduced C*-algebra and for the Fourier algebra of such groups. Our
method further implies that the kernel of the comparison map between the
bounded and the usual group cohomology in degree 2 has a basis of power
continuum. The present work can be viewed as a first non-trivial step towards a
systematic investigation of direct limits of hyperbolic groups.Comment: 40 pages, 8 figure
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