reserve G for _Graph;
reserve V for non empty set, E for Relation of V;
reserve E for symmetric Relation of V;
reserve G for GraphFromSymRel of V, E;

theorem
  for X, Y being set holds G.edgesBetween(X,Y) c= Y|`E|X \/ X|`E|Y
proof
  let X, Y be set;
  Y|`E|X \/ X|`E|Y = createGraph(V,E).edgesBetween(X,Y) by Th77;
  hence thesis by GLIB_000:77;
end;
