fact: Definition contract_ctree cf := let cp := cfprog cf in let cm := cfcontract_mask cf in if cfctr (nseq (cprsize cp) false) cm cp is Some cpc then if valid_ctrm cm cp then Some (cpcolor cpc) else None else None.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color coloring cfmap ctree) fourcolor(cfcolor)