reserve G,G1,G2 for _Graph;
reserve e,x,y for set;
reserve v,v1,v2 for Vertex of G;
reserve W for Walk of G;

theorem
  for C being Component of G, v being Vertex of G holds v in
  the_Vertices_of C iff the_Vertices_of C = G.reachableFrom(v) by Lm16;
