@incollection{Flatto1992,
  author    = {{Leopold Flatto}},
  title     = {{$Z$-numbers and $\beta$-transformations}},
  booktitle = {{Symbolic dynamics and its applications (New Haven, CT, 1991)}},
  publisher = {{American Math. Soc., Providence, RI}},
  year      = {{1992}},
  volume    = {{135}},
  pages     = {{181--201}},
  note      = {{MR94c:11065}},
}