ナプキンリング問題
Devlin, Keith (2008), The Napkin Ring Problem, Mathematical Association of America, オリジナルの11 August 2011時点におけるアーカイブ。, https://webcitation.org/60rIio0jC
Devlin, Keith (2008), Lockhart's Lament, Mathematical Association of America, オリジナルの11 August 2011時点におけるアーカイブ。, https://webcitation.org/60rJGphT5
Gardner, Martin (1994), “Hole in the Sphere”, My best mathematical and logic puzzles, Dover Publications, p. 8
Jones, Samuel I. (1912), Mathematical Wrinkles for Teachers and Private Learners, Norwood, MA: J. B. Cushing Co. Problem 132 asks for the volume of a sphere with a cylindrical hole drilled through it, but does not note the invariance of the problem under changes of radius.