Julie Johnson-Pynn, Dorothy M. Fragaszy, Elizabeth M. Hirsh, Karen E. Brakke, Patricia M. Greenfield,
Strategies used to combine seriated cups by chimpanzees (Pan troglodytes), bonobos (Pan paniscus), and capuchins (Cebus apella). Journal of Comparative Psychology. ,vol. 113, pp. 137- 148 ,(1999) ,
10.1037/0735-7036.113.2.137