reserve k,n for Nat,
  x,y,z,y1,y2 for object,X,Y for set,
  f,g for Function;
reserve p,q,r,s,t for XFinSequence;
reserve D for set;

theorem Th14:
  for D be set holds {} is XFinSequence of D
proof
  let D be set;
  rng {} c= D;
  hence thesis by RELAT_1:def 19;
end;
