fact: Definition excluded_arity n := reducibility -> forall G x, @valid_hub G x -> (arity x == n) = false.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph bigop ssralg ssrnum ssrint) fourcolor(hypermap geometry patch coloring birkhoff embed) fourcolor(quiz quiztree part redpart discharge hubcap) fourcolor(cfmap cfcontract cfreducible configurations)