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@book{peebles1993,
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@article{clowe2006,
  author  = {Clowe, D. and Brada\v{c}, M. and Gonzalez, A. H. and Markevitch, M. and Randall, S. W. and Jones, C. and Zaritsky, D.},
  title   = {A Direct Empirical Proof of the Existence of Dark Matter},
  journal = {Astrophysical Journal Letters},
  volume  = {648},
  pages   = {L109--L113},
  year    = {2006}
}