@article{PawelkeButzer2007,
  author    = {Siegfried Pawelke and Paul L. Butzer},
  title     = {Semi-groups and resolvent operators},
  journal   = {Archive for Rational Mechanics and Analysis},
  volume    = {30},
  number    = {2},
  pages     = {127 -- 147},
  doi       = {10.1007/BF00250941},
  year      = {2007},
}