theorem Th6:
  (0.X,0.X) to_power n=0.X
proof
  defpred P[set] means for m holds m=$1 & m<= n implies (0.X,0.X) to_power m =
  0.X;
A1: for k st P[k] holds P[k+1] by Th5;
A2: P[0] by Th1;
  for n holds P[n] from NAT_1:sch 2(A2,A1);
  hence thesis;
end;
