fact: Definition drule27 := Part $ 7+ $ 6 $[6 5 6+] 7 $ 7 $[5] 6- $ * $ * $.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) mathcomp(bigop order ssralg ssrnum ssrint) fourcolor(hypermap geometry part)