[X-ray quiz series I, sequence 6, cases 20-22].

@article{Haemmerli1975XrayQS,
  title={[X-ray quiz series I, sequence 6, cases 20-22].},
  author={Urs Peter Haemmerli and Patrick Peter and U S von B{\"u}ren and Emanuele Maranta and Andr{\'e} Louis Blum},
  journal={Leber, Magen, Darm},
  year={1975},
  volume={5 6},
  pages={245, 275-7}
}