
theorem
  1987 is prime
proof
  now
    1987 = 2*993 + 1; hence not 2 divides 1987 by NAT_4:9;
    1987 = 3*662 + 1; hence not 3 divides 1987 by NAT_4:9;
    1987 = 5*397 + 2; hence not 5 divides 1987 by NAT_4:9;
    1987 = 7*283 + 6; hence not 7 divides 1987 by NAT_4:9;
    1987 = 11*180 + 7; hence not 11 divides 1987 by NAT_4:9;
    1987 = 13*152 + 11; hence not 13 divides 1987 by NAT_4:9;
    1987 = 17*116 + 15; hence not 17 divides 1987 by NAT_4:9;
    1987 = 19*104 + 11; hence not 19 divides 1987 by NAT_4:9;
    1987 = 23*86 + 9; hence not 23 divides 1987 by NAT_4:9;
    1987 = 29*68 + 15; hence not 29 divides 1987 by NAT_4:9;
    1987 = 31*64 + 3; hence not 31 divides 1987 by NAT_4:9;
    1987 = 37*53 + 26; hence not 37 divides 1987 by NAT_4:9;
    1987 = 41*48 + 19; hence not 41 divides 1987 by NAT_4:9;
    1987 = 43*46 + 9; hence not 43 divides 1987 by NAT_4:9;
  end;
  then for n being Element of NAT st 1 < n & n*n <= 1987 & n is prime
  holds not n divides 1987 by XPRIMET1:28;
  hence thesis by NAT_4:14;
end;
