Ernst Snapper所著The Three Crises in Mathematics: Logicism, Intuitionism, and Formalism, MathematicsMagazine, Vol. 52 (1979), pp. 207-216這篇得獎論文(美國數學協會MAA
Association of America Recreational MathematicsMagazineThe. [2018-11-30]. (原始内容存档于2021-01-17). Recreational Mathematics (页面存档备份,存于互联网档案馆) from MathWorld