reserve x,y for set,
  n for Nat;

theorem Th5:
  for f be non empty FinSequence of NAT,D be non empty
  disjoint_with_NAT set holds FreeGenSetNSG(f,D) is non empty
proof
  let f be non empty FinSequence of NAT,D be disjoint_with_NAT non empty set;
  set X = DTConUA(f,D);
  set d = the Element of D;
  reconsider d1 = d as Symbol of X by XBOOLE_0:def 3;
  Terminals X = D by Th3;
  then root-tree d1 in {root-tree k where k is Symbol of X: k in Terminals X};
  hence thesis;
end;
