1. Some new approaches to the study of obsidian trade in the Mediterranean and adjacent areas;Ammerman,1977
2. Trade competition and artefact distribution;Bradley;World Archaeology,1971
3. Distance and human interaction;Claeson;Geografisker Annaler B,1968
4. Obsidian in the West Mediterranean;Hallam;Proceedings of the Prehistoric Society,1976
5. Application of exponential distance decay to human and animal activities;Haynes;Geografisker Annaler B,1974