fact: Record drule_fork := DruleFork { source_drules : drules; target_drules : drules; _ : drule_fork_values source_drules target_drules }.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) mathcomp(bigop order ssralg ssrnum ssrint) fourcolor(hypermap geometry part)