Keller's Conjecture
Keller conjectured that tiling an 
-D space with -D Hypercubes of equal size yields anarrangement in which at least two hypercubes have an entire 
-D ``side'' in common. The Conjecture has been proven true for 
to 6, but disproven for 
.
References
Cipra, B. ``If You Can't See It, Don't Believe It.'' Science 259, 26-27, 1993. Cipra, B. What's Happening in the Mathematical Sciences, Vol. 1. Providence, RI: Amer. Math. Soc., pp. 24, 1993.
- Arithmetic Mean
- Arithmetic Progression
- Arithmetic Sequence
- Arithmetic Series
- Armstrong Number
- Arnold Diffusion
- Arnold's Cat Map
- Arnold Tongue
- Aronhold Process
- Aronson's Sequence
- Arrangement
- Arrangement Number
- Array
- Arrowhead Curve
- Arrow Notation
- Arrow's Paradox
- Art Gallery Theorem
- Articulation Vertex
- Artin Braid Group
- Artinian Group
- Artinian Ring
- Artin L-Function
- Artin Reciprocity
- Artin's Conjecture
- Artin's Constant