
theorem
  239 is prime
proof
  now
    239 = 2*119 + 1; hence not 2 divides 239 by NAT_4:9;
    239 = 3*79 + 2; hence not 3 divides 239 by NAT_4:9;
    239 = 5*47 + 4; hence not 5 divides 239 by NAT_4:9;
    239 = 7*34 + 1; hence not 7 divides 239 by NAT_4:9;
    239 = 11*21 + 8; hence not 11 divides 239 by NAT_4:9;
    239 = 13*18 + 5; hence not 13 divides 239 by NAT_4:9;
  end;
  then for n being Element of NAT st 1 < n & n*n <= 239 & n is prime
  holds not n divides 239 by XPRIMET1:12;
  hence thesis by NAT_4:14;
