@inproceedings{ijcai1975p13,
  title     = {An Extension of Unification to Substitution with an Application to Automatic Theorem Proving},
  author    = {van Vaalen, J.},
  booktitle = {Proceedings of the Fourth International Joint Conference on
               Artificial Intelligence, {IJCAI-75}},
  publisher = {International Joint Conferences on Artificial Intelligence},
  editor    = {Patrick Winston and Carl Hewitt},
  pages     = {77--81},
  year      = {1975},
  note      = {Mathematical and Theoretical Aspects of A.I},
  url       = {https://ijcai.org/proceedings/1975/13},
}