The story
The conjecture was introduced by Ott-Heinrich Keller (1930).
Etymology from Wiktionary, CC BY-SA 4.0.
Keller's conjecture
Today it means: The conjecture that, in any tiling of n-dimensional Euclidean space by identical hypercubes, there are two hypercubes that share an entire (n − 1)-dimensional face with each other. Full definition →