
theorem
  73 is prime
proof
  now
    73 = 2*36 + 1; hence not 2 divides 73 by NAT_4:9;
    73 = 3*24 + 1; hence not 3 divides 73 by NAT_4:9;
    73 = 5*14 + 3; hence not 5 divides 73 by NAT_4:9;
    73 = 7*10 + 3; hence not 7 divides 73 by NAT_4:9;
  end;
  then for n being Element of NAT st 1 < n & n*n <= 73 & n is prime
  holds not n divides 73 by XPRIMET1:8;
  hence thesis by NAT_4:14;
end;
