Resolving Pisanski's Conjecture

Abstract

We prove Pisanski's conjecture on quadrilateral embeddings of regular bipartite graphs. For integers $m\geq d\geq4$ with $4\mid md$, we construct both a connected simple $d$-regular bipartite graph $G$ with $m$ vertices in each bipartition class and an orientable quadrangulation. This graph's genus is \[ \ga(G)=1+\frac{m(d-4)}4. \] These quadrangulations attain the lower bound on the genus from Euler's formula. We give dihedral constructions for even $m$ and a cyclic construction for every $m\geq d$ with $4\mid d$. In each case, two cyclic permutations of a connection set of size $d$ determine all of the local rotations.