1. S.Kohjiya and Y.Ikeda , Chemistry, manufacture, and applications of natural rubber , Woodhead Publishing , 2021
2. Prehistoric Polymers: Rubber Processing in Ancient Mesoamerica
3. T.Leyenaar and L.Parsons , Ulama, The Ballgame of the Mayas and Aztecs, Spruyt , Van Mantgem and De Does , Leiden, Netherlands , 1988
4. V.Scarborough and D.Wilcox , The Mesoamerican Ball Game , Univ. of Arizona Press , Tucson , 1991
5. S.Kohjiya , Ten-nen Gomu no Rekisi , in History of Natural Rubber , Kyoto University Press , 2013