@unpublished{BelagaMignotte2000,
  author    = {{Edward Belaga and Maurice Mignotte}},
  title     = {{Cyclic Structure of Dynamical Systems Associated with $3x+d$ Extensions of Collatz Problem}},
  year      = {{2000}},
  url       = {{http://hal.archives-ouvertes.fr/IRMA-ACF}},
  note      = {{U. Strasbourg report 2000-18, 57 pages}},
}