M. F. Arias Holgado, F. Fernández Serra, L. E. Gomez Sancho, R. J. Martínez Cervantes, and M. E. Trigo Sanchez, “A conceptual approach to the uses of the term play”, Apunt. Psic., vol. 8, no. 31, pp. 28–31, Jul. 1990, doi: 10.55414/ap.v9i31.1078.