Relative Length of Long Paths and Cycles in Graphs

Abstract

For a graph $G$, $n$ denotes the order of $G$, $p$ the order of a longest path in $G$ and $c$ the order of a longest cycle. We show that if $G$ is a 2-connected graph such that $d(x)+d(y)+d(z)\ge p+2$ for all triples $x,y,z$ of independent vertices, then $c\ge p-1$. This improves results of Nash-Williams (in terms of minimum degree $\delta$ and order $n$), Bondy (in terms of degree sum $\sigma_{3}$ and order $n$), and Enomoto, Heuvel, Kaneko and Saito (in terms of degree sum $\sigma_3$, order $n$ and relative length $diff(G)=p-c$).