reserve k for Nat;
reserve p for Prime;

theorem
  p*p <= k < 121 implies p = 2 or p = 3 or p = 5 or p = 7
  proof
    assume p*p <= k < 121;
    then p*p < 11*11 by XXREAL_0:2;
    hence thesis by Ttool11a,NAT_4:1;
  end;
