
theorem Th54:
  for G being _Graph, v1, v2 being Vertex of G
  holds v1 in G.reachableFrom v2 implies v2 in G.reachableFrom v1
proof
  let G be _Graph, v1, v2 be Vertex of G;
  assume v1 in G.reachableFrom v2;
  then G.reachableFrom v2 = G.reachableFrom v1 by GLIB_002:12;
  hence thesis by GLIB_002:9;
end;
