fact: Definition adj_index := {ij : Ir * Ir | ij.1 < ij.2}%N.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph order ssralg ssrnum ssrint) fourcolor(hypermap geometry color coloring patch snip grid) fourcolor(matte)