# On the Strong Hanani-Tutte Theorem

### Abstract

A graph is planar if it has a drawing in which no two edges cross. The Hanani-Tutte Theorem states that a graph is planar if it has a drawing $D$ such that any two edges in $D$ cross an even number of times.

A graph $G$ is a non-separating planar graph if it has a drawing $D$ such that (1) edges do not cross in $D$, and (2) for any cycle $C$ and any two vertices $u$ and $v$ that are not in $C$, $u$ and $v$ are on the same side of $C$ in $D$. Non-separating planar graphs are closed under taking minors and hence have a finite forbidden minor characterisation.

In this paper, we prove a Hanani-Tutte type theorem for non-separating planar graphs. We use this theorem to prove a stronger version of the strong Hanani-Tutte Theorem for planar graphs, namely that a graph is planar if it has a drawing in which any two disjoint edges cross an even number of times or it has a chordless cycle that enables a suitable decomposition of the graph.