Ideal (Partial Order)
An ideal 
of a Partial Order 
is a subset of the elements of which satisfy the property thatif 
and 
, then 
. For 
disjoint chains in which the 
th chain contains 
elements,there are 
ideals. The number of ideals of a 
-element Fence Poset is theFibonacci Number 
.
References
Ruskey, F. ``Information on Ideals of Partially Ordered Sets.'' http://sue.csc.uvic.ca/~cos/inf/pose/Ideals.html. Steiner, G. ``An Algorithm to Generate the Ideals of a Partial Order.'' Operat. Res. Let. 5, 317-320, 1986.
- Angular Defect
- Angular Distance
- Angular Velocity
- Anharmonic Ratio
- Anisohedral Tiling
- Annihilator
- Annulus
- Annulus Conjecture
- Annulus Theorem
- Anomalous Cancellation
- Anomalous Number
- Anonymous
- Anosov Automorphism
- Anosov Diffeomorphism
- Anosov Flow
- Anosov Map
- ANOVA
- Anthropomorphic Polygon
- Anthyphairetic Ratio
- Antiautomorphism
- Anticevian Triangle
- Antichain
- Anticlastic
- Anticommutative
- Anticommutator