fact: Definition drule19 := Part $ 6 $ 6+ $ 8+ $[5] 5 $[5] 6 $ 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)