Reconstruction of graded groupoids from graded Steinberg algebras

We show how to reconstruct a graded ample Hausdorff groupoid with topologically principal neutrally-graded component from the ring structure of its graded Steinberg algebra over any commutative integral domain with 1, together with the embedding of the canonical abelian subring of functions supported on the unit space. We deduce that diagonal-preserving ring isomorphism of Leavitt path algebras implies $C^*$-isomorphism of $C^*$-algebras for graphs $E$ and $F$ in which every cycle has an exit. This is a joint work with Joan Bosa, Roozbeh Hazrat and Aidan Sims.Universidad de Málaga. Campus de Excelencia internacional Andalucía Tec

Path graphs

The concept of a line graph is generalized to that of a path graph. The path graph Pk(G) of a graph G is obtained by representing the paths Pk in G by vertices and joining two vertices whenever the corresponding paths Pk in G form a path Pk+1 or a cycle Ck. P3-graphs are characterized and investigated on isomorphism and traversability. Trees and unicyclic graphs with hamiltonian P3-graphs are characterized

Isomorphisms and traversability of directed path graphs

The concept of a line digraph is generalized to that of a directed path graph. The directed path graph \forw P_k(D) of a digraph $D$ is obtained by representing the directed paths on $k$ vertices of $D$ by vertices. Two vertices are joined by an arc whenever the corresponding directed paths in $D$ form a directed path on $k+1$ vertices or form a directed cycle on $k$ vertices in $D$. In this introductory paper several properties of \forw P_3(D) are studied, in particular with respect to isomorphism and traversability. In our main results, we characterize all digraphs $D$ with \forw P_3(D)\cong D, we show that \forw P_3(D_1)\cong\forw P_3(D_2) ``almost always'' implies $D_1\cong D_2$, and we characterize all digraphs with Eulerian or Hamiltonian \forw P_3-graphs

On the Lengths of Symmetry Breaking-Preserving Games on Graphs

Given a graph $G$, we consider a game where two players, $A$ and $B$, alternatingly color edges of $G$ in red and in blue respectively. Let $l(G)$ be the maximum number of moves in which $B$ is able to keep the red and the blue subgraphs isomorphic, if $A$ plays optimally to destroy the isomorphism. This value is a lower bound for the duration of any avoidance game on $G$ under the assumption that $B$ plays optimally. We prove that if $G$ is a path or a cycle of odd length $n$, then $\Omega(\log n)\le l(G)\le O(\log^2 n)$. The lower bound is based on relations with Ehrenfeucht games from model theory. We also consider complete graphs and prove that $l(K_n)=O(1)$.Comment: 20 page