Permissive nominal terms and their unification: an infinite, co-infinite approach to nominal techniques

@article{Dowek2010PermissiveNT,
  title={Permissive nominal terms and their unification: an infinite, co-infinite approach to nominal techniques},
  author={Gilles Dowek and Murdoch James Gabbay and Dominic P. Mulligan},
  journal={Log. J. IGPL},
  year={2010},
  volume={18},
  pages={769-822}
}
Nominal terms extend first-order terms with binding. They lack some properties of first- and higher-order terms: Terms must be reasoned about in a context of ‘freshness assumptions’; it is not always possible to ‘choose a fresh variable symbol’ for a nominal term; it is not always possible to ‘α-convert a bound variable symbol’ or to ‘quotient by α-equivalence’; the notion of unifier is not based just on substitution. Permissive nominal terms closely resemble nominal terms but they recover… 

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