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 Th12:
  for D being non empty set ex p being XFinSequence of D st len p = k
proof
  let D be non empty set;
  set y = the Element of D;
  set p = k --> y;
  reconsider p = k --> y as XFinSequence;
  reconsider p as XFinSequence of D;
  take p;
  thus thesis;
end;
