@article{Grotendorst1990,
  author    = {Grotendorst, Johannes},
  title     = {Approximating functions by means of symbolic computation and a general extrapolation method},
  series = {Computer Physics Communications. 59 (1990), H. 2},
  journal   = {Computer Physics Communications. 59 (1990), H. 2},
  isbn      = {0010-4655},
  pages     = {289 -- 301},
  year      = {1990},
  language  = {en}
}
@article{ZiemonsHerzogFeinendegen1990,
  author    = {Ziemons, Karl and Herzog, H. and Feinendegen, L. E.},
  title     = {Iterative image reconstruction with weighted pixel contribution to projection element},
  series = {European Journal of Nuclear Medicine},
  volume    = {16},
  journal   = {European Journal of Nuclear Medicine},
  number    = {7},
  isbn      = {1619-7089},
  pages     = {403 -- 403},
  year      = {1990},
  language  = {en}
}