reserve FT for non empty RelStr;
reserve x, y, z for Element of FT;

theorem
  for FT being filled non empty RelStr holds the set of all U_FT x where x is
  Element of FT  is Cover of FT
proof
  let FT be filled non empty RelStr;
  let a be object;
  assume a in the carrier of FT;
  then reconsider b = a as Element of FT;
  b in U_FT b & U_FT b in the set of all U_FT x where x is Element of FT
 by Def4;
  hence thesis by TARSKI:def 4;
end;
