
theorem
  for G being _Graph
  holds G is vertex-finite iff ex n being non zero Nat st G is n-vertex
proof
  let G be _Graph;
  hereby
    assume G is vertex-finite;
    then reconsider n = card the_Vertices_of G as Nat;
    reconsider n as non zero Nat;
    take n;
    thus G is n-vertex;
  end;
  thus thesis;
end;
