@article{Benini2016,
  author    = {Marco Benini},
  title     = {Optimal space of linear classical observables for Maxwell k-forms via spacelike and timelike compact de Rham cohomologies},
  journal   = {Journal of mathematical physics},
  volume    = {57},
  pages     = {1249 -- 1279},
  doi       = {10.1063/1.4947563},
  year      = {2016},
}