theorem Th22:
  for G being _trivial _Graph holds ex v being Vertex of G st
  the_Vertices_of G = {v}
proof
  let G be _trivial _Graph;
  card (the_Vertices_of G) = 1 by Def19;
  then consider v being object such that
A1: the_Vertices_of G = {v} by CARD_2:42;
  reconsider v as Vertex of G by A1,TARSKI:def 1;
  take v;
  thus thesis by A1;
end;
