@article{Bordihn2017,
  author    = {Henning Bordihn},
  title     = {Active symbols in grammars with valuations},
  journal   = {Theoretical computer science},
  volume    = {682},
  pages     = {42 -- 48},
  doi       = {10.1016/j.tcs.2016.11.008},
  year      = {2017},
}