Empty Set
The Set containing no elements, denoted 
. Strangely, the empty set is both Open andClosed for any Set 
and Topology. A Groupoid, Semigroup, Quasigroup,Ringoid, and Semiring can be empty. A Monoid, Group, and Rings must have at least oneelement, while Division Rings and Fields must have at least two elements.
References
Conway, J. H. and Guy, R. K. The Book of Numbers. New York: Springer-Verlag, p. 266, 1996.
- Hofstadter Point
- Hofstadter Sequences
- Hofstadter's Q-Sequence
- Hofstadter Triangle
- Hole
- Holomorphic Function
- Holonomic Constant
- Holonomic Function
- Holonomy
- Homeoid
- Homeomorphic
- Homeomorphic Group
- Homeomorphic Type
- Homeomorphism
- Home Plate
- HOMFLY Polynomial
- Homoclinic Point
- Homogeneous Coordinates
- Homogeneous Function
- Homogeneous Numbers
- Homogeneous Polynomial
- Homographic
- Homography
- Homological Algebra
- Homologous Points