$ (see Figures \[fig:0\] and \[fig:0\]).  at (0,0) ; at (0,0) ; at (0,0) ; at (0,0) ;  (0,0)-(0,0)-(0,0.0)-(0,0.0)-(0,0)-(0,0)-(0,0.0)-(0,0.0); at (0.0,0.0) [$H_0$]{}; at (0.0,0.00) [$H_0$]{}; at (0.0,0.00) [$H_0$]{}; at (0.0,0.00) [$H_0$]{}; at (