@ARTICLE{havlicek,
  author = {Hans Havlicek and Karl Svozil},
  title = {Density conditions for quantum propositions},
  journal = {Journal of Mathematical Physics},
  year = {1996},
  volume = {37},
  pages = {5337-5341},
  number = {11},
  month = {November},
  doi = {10.1063/1.531738},
  url = {http://dx.doi.org/10.1063/1.531738}
}