fact: Definition hubcap_cover hc := let b := (dboundK nhub *+ 2 - 1)%R in let v := tally_hubcap hc in [&& size v == nhub, 0 \notin v & hubcap_cover_rec v b hc].
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)