Gallai's Path Decomposition of Levi Graph

Abstract

Gallai's path decomposition conjecture states that for a connected graph $G$ on $n$ vertices, there exist a path decomposition of size $\lceil \frac{n}{2} \rceil$. Levi graph of order one, denoted by $L_{1}(m,k)$ is a bipartite graph having vertex partition $(A,B)$, where $A$ is the collection of all $k-1$ subsets of $[m]$ and $B$ is the collection of all $k$ subsets of $[m]$. In this graph a $k-1$ set is adjacent to a $k$ set if it is properly contained inside the $k$ set. Path number of a graph $G$ is the minimum size of its path decomposition. Hence, we can rewrite the Gallai conjecture as the path number of a connected graph is at most $\lceil \frac{n}{2} \rceil$. In this work we prove conjecture on $L_{1}(m,k)$ for all $m \ge 2 $, $2 \le k \le m$. Moreover determines the path number of $L_{1}(m,2)$ for all $m$.