Fault tolerance of vertex pancyclicity in alternating group graphs

We study fault tolerance of vertex k pancyclicity of the alternating group graph AGn. A graph G is vertex k pancyclic, if for every vertex p∈G, there is a cycle going through p of every length from k to |G|. Xue and Liu [Z.-J. Xue, S.-Y. Liu, An optimal result on fault-tolerant cycle-embedding in alternating group graphs, Inform. Proc. Lett. 109 (2009) 1197-1201] put the conjecture that AGn is (2n-7)-fault-tolerant vertex pancyclic, which means that if the number of faults |F|⩽2n-7, then AGn-F is still vertex pancyclic. Chang and Yang [J.-M. Chang, J.-S. Yang, Fault-tolerant cycle-embedding in alternating group graphs, Appl. Math. Comput. 197 (2008) 760-767] showed that for the shortest cycles the fault-tolerance of AGn is much lower. They noted that with n-2 faults one can cut all 3-cycles going through a given vertex p (it is easy to observe that the same set of faults cuts all 4- and 5-cycles going through p). On the other hand they show that AGn is n-3-fault tolerant vertex 3 pancyclic. In this paper we show that the cycles of length ⩾6 are much more fault-tolerant. More precisely, we show that AGn is (2n-6)-fault-tolerant vertex 6 pancyclic. This bound is optimal, because every vertex p has 2n-4 neighbors.