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 G being non _trivial _finite acyclic _Graph st the_Edges_of G <> {}
  holds ex v1,v2 being Vertex of G st v1 <> v2 & v1 is endvertex & v2 is
  endvertex & v2 in G.reachableFrom(v1) by Lm23;
