reserve k for Nat;
reserve p for Prime;

theorem
  p*p <= k < 169 implies p = 2 or p = 3 or p = 5 or p = 7 or p = 11
  proof
    assume p*p <= k < 169;
    then p*p < 13*13 by XXREAL_0:2;
    hence thesis by Ttool13a,NAT_4:1;
  end;
