Butler, G. D. (1936). Playgrounds, their administration and operation: National recreation association. A.S. Barnes.
Chicago-referens (17:e uppl.)Butler, George D. Playgrounds, Their Administration and Operation: National Recreation Association. New York: A.S. Barnes, 1936.
MLA-referens (8:e uppl.)Butler, George D. Playgrounds, Their Administration and Operation: National Recreation Association. A.S. Barnes, 1936.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.