Eulerian circuits and path decompositions in quartic planar graphs

A subcycle of an Eulerian circuit is a sequence of edges that are consecutive in the circuit and form a cycle. We characterise the quartic planar graphs that admit Eulerian circuits avoiding 3-cycles and 4-cycles. From this, it follows that a quartic planar graph of order $n$ can be decomposed into $k_1+k_2+k_3+k_4$ many paths with $k_i$ copies of $P_{i+1}$, the path with $i$ edges, if and only if $k_1+2k_2+3k_3+4k_4 = 2n$. In particular, every connected quartic planar graph of even order admits a $P_5$-decomposition.