fact: Definition smerge2_rel := [rel u v : smerge2_vertex | if (val u == x) && (val v != x) then val v -- x || val v -- y else if (val v == x) && (val u != x) then val u -- x || val u -- y else val u -- val v].
imports: mathcomp(all_ssreflect) GraphTheory(edone preliminaries digraph sgraph) GraphTheory(connectivity minor treewidth arc set_tac)