Sidon Sets in Groups and Induced Subgraphs of Cayley Graphs

Let S be a subset of a group G. We call S a Sidon subset of the first (second) kind, if for any x, y, z, w ∈ S of which at least 3 are different, xy ≠ zw (xy-1 ≠ zw-1, resp.). (For abelian groups, the two notions coincide.) If G has a Sidon subset of the second kind with n elements then every n-vertex graph is an induced subgraph of some Cayley graph of G. We prove that a sufficient condition for G to have a Sidon subset of order n (of either kind) is that (❘G❘ ⩾ cn3. For elementary Abelian groups of square order, ❘G❘ ⩾ n2 is sufficient. We prove that most graphs on n vertices are not induced subgraphs of any vertex transitive graph with <cn2/log2n vertices. We comment on embedding trees and, in particular, stars, as induced subgraphs of Cayley graphs, and on the related problem of product-free (sum-free) sets in groups. We summarize the known results on the cardinality of Sidon sets of infinite groups, and formulate a number of open problems.We warn the reader that the sets considered in this paper are different from the Sidon sets Fourier analysts investigate

Monoid graphs and generalized Petersen graphs

Treballs Finals de Grau de Matemàtiques, Facultat de Matemàtiques, Universitat de Barcelona, Any: 2023, Director: Kolja Knauer[en] First, a wide definition of Cayley graphs is presented. We focus on the notion of monoid graph: a graph is a monoid graph if it is isomorphic to the underlying graph of the Cayley graph $\operatorname{Cay}(M, C)$ of some monoid $M$ with some connection set $C \subseteq M$. Secondly, the family of Generalized Petersen Graphs $G(n, k)$ is presented. We study the open question whether every Generalized Petersen Graph is a monoid graph, and we focus on the smallest one for which the question remains unanswered: $G(7,2)$. Finally, we explore the feasibility of using the computer to search for a possible monoid for $G(7,2)$. We conclude that it is not viable to check all the possibilities with the proposed algorithms. Nevertheless, we are able to provide a computer-assisted proof that if $G(7,2)$ is a monoid graph then the connection set $C$ does not have any invertible element