fact: Definition ecpA_edge x := if ~~ cface (edge x0) (node x0) then edge x else if x == x0 then edge (node (node x0)) else if x == node (node x0) then edge x0 else edge x.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)