reserve a,b,i,k,m,n for Nat;
reserve s,z for non zero Nat;
reserve c for Complex;

theorem Th15:
  881 is prime
  proof
    for n being Element of NAT holds 1 < n & n*n <= 881 & n is prime implies
    not n divides 881
    proof
      let n be Element of NAT;
      881 = 2*440 + 1;
      then
A1:   not 2 divides 881;
      881 = 3*293 + 2;
      then
A2:   not 3 divides 881 by NAT_4:9;
      881 = 5*176 + 1;
      then
A3:   not 5 divides 881 by NAT_4:9;
      881 = 7*125 + 6;
      then
A4:   not 7 divides 881 by NAT_4:9;
      881 = 11*80 + 1;
      then
A5:   not 11 divides 881 by NAT_4:9;
      881 = 13*67 + 10;
      then
A6:   not 13 divides 881 by NAT_4:9;
      881 = 17*51 + 14;
      then
A7:   not 17 divides 881 by NAT_4:9;
      881 = 19*46 + 7;
      then
A8:   not 19 divides 881 by NAT_4:9;
      881 = 23*38 + 7;
      then
A9:   not 23 divides 881 by NAT_4:9;
      881 = 29*30 + 11;
      then
      not 29 divides 881 by NAT_4:9;
      hence thesis by A1,A2,A3,A4,A5,A6,A7,A8,A9,Th12;
    end;
    hence thesis by NAT_4:14;
  end;
