
theorem
  13 is Proth
  proof
A1:  2|^2 = 2|^(1+1) .= 2|^1 * 2 by NEWTON:6 .= 2 * 2;
    3 = 2 * 1 + 1; then
    reconsider e = 3 as odd Nat;
    take e,2;
    thus thesis by A1;
  end;
