fact: Definition hubcap_rot j := rot_part (if j is j'.+2 then j' else nhub + j - 2).
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) mathcomp(bigop order ssralg ssrnum ssrint) fourcolor(hypermap geometry quiztree part discharge)