\bibitem{Halsey86}     T.C.Halsey, M.H.Jensen, L.P.Kadanoff, I.Procaccia, B.I.Shraiman   \hskip 2mm
                       {\it Fractal Measures and Their Singularities: The Characterization of Strange Sets},
                       Phys.Rev. A{\bf 33}, 1141-1151, 1986.