theorem Th24:
  for f be Sequence holds
  base-f = 0 & limit-f = dom f & len-f = dom f
  proof
    let f be Sequence;
    per cases;
    suppose f = {};
      hence thesis by Th15;
    end;
    suppose
A1:   f <> {};
      (dom f)\0 = dom f;
      hence base-f = 0 & limit-f = dom f by A1,Th23;
      hence len-f = dom f by ORDINAL3:56;
    end;
  end;
