fact: Definition check_reducible := oapp (ctree_disjoint (Kempe_tree (cfprog cf))) false (contract_ctree cf).
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color chromogram coloring kempe) fourcolor(cfmap cfcolor cfcontract ctree kempetree)