
theorem
  211 is prime
proof
  now
    211 = 2*105 + 1; hence not 2 divides 211 by NAT_4:9;
    211 = 3*70 + 1; hence not 3 divides 211 by NAT_4:9;
    211 = 5*42 + 1; hence not 5 divides 211 by NAT_4:9;
    211 = 7*30 + 1; hence not 7 divides 211 by NAT_4:9;
    211 = 11*19 + 2; hence not 11 divides 211 by NAT_4:9;
    211 = 13*16 + 3; hence not 13 divides 211 by NAT_4:9;
  end;
  then for n being Element of NAT st 1 < n & n*n <= 211 & n is prime
  holds not n divides 211 by XPRIMET1:12;
  hence thesis by NAT_4:14;
