@inproceedings{kay-sag:2009,
  author    = {Kay, Paul and Sag, Ivan A.},
  title     = {How hard a problem would this be to solve?},
  booktitle = {{Proceedings of the 16th International Conference on Head-Driven Phrase Structure Grammar, Georg-August-Universität Göttingen, Germany}},
  editor    = {Müller, Stefan},
  OPTissn   = {15351793},
  doi       = {10.21248/hpsg.2009.9},
  publisher = {CSLI Publications},
  address   = {Stanford, CA},
  pages     = {171--191},
  year      = {2009},
}

@inproceedings{kay-sag:2009-cr,
  crossref  = {HPSG2009},
  author    = {Kay, Paul and Sag, Ivan A.},
  title     = {How hard a problem would this be to solve?},
  doi       = {10.21248/hpsg.2009.9},
  pages     = {171--191},
}

@proceedings{HPSG2009,
  editor    = {Müller, Stefan},
  title     = {{Proceedings of the 16th International Conference on Head-Driven Phrase Structure Grammar, Georg-August-Universität Göttingen, Germany}},
  booktitle = {{Proceedings of the 16th International Conference on Head-Driven Phrase Structure Grammar, Georg-August-Universität Göttingen, Germany}},
  publisher = {CSLI Publications},
  address   = {Stanford, CA},
  OPTissn   = {15351793},
  year      = {2009},
}