fact: Record preembedding : Prop := Preembedding { preembedding_face : {in A, {morph h: x / face x}}; preembedding_arity : {in A, {mono h: x / order face x}}; preembedding_cover : A \subset fclosure face edge_central; preembedding_rlinked : rlink_connected [predI A & edge_central] }.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap walkup geometry color chromogram)