Gallai's path decomposition in planar graphs

Alexandre Blanché, Marthe Bonamy, Nicolas Bonichon

Published 2021-10-17, updated 2022-06-21Version 2

In 1968, Gallai conjectured that the edges of any connected graph with $n$ vertices can be partitioned into $\lceil \frac{n}{2} \rceil$ paths. We show that this conjecture is true for every planar graph. More precisely, we show that every connected planar graph except $K_3$ and $K_5^-$ ($K_5$ minus one edge) can be decomposed into $\lfloor \frac{n}{2} \rfloor$ paths.