@misc{indiciaed6baa54db5ff,
  title = {Does conditional discrimination learning by pigeons necessarily involve hierarchical relationships?},
  author = {D R Thomas and E K Schmidt},
  year = {1989},
  doi = {10.1901/jeab.1989.52-249},
  url = {https://pubmed.ncbi.nlm.nih.gov/16812596/},
  note = {Source identifier: 16812596}
}