Intrinsically Linked
A Graph is intrinsically linked if any embedding of it in 3-D contains a nontrivialLink. A Graph is intrinsically linked Iff it contains one of the sevenPetersen Graphs (Robertson et al. 1993).
The Complete Graph 
(left) is intrinsically linked because it contains at least two linkedTriangles. The Complete k-Partite Graph 
(right) isalso intrinsically linked.
References
Adams, C. C. The Knot Book: An Elementary Introduction to the Mathematical Theory of Knots. New York: W. H. Freeman, pp. 217-221, 1994. Robertson, N.; Seymour, P. D.; and Thomas, R. ``Linkless Embeddings of Graphs in 3-Space.'' Bull. Amer. Math. Soc. 28, 84-89, 1993.
- Apothem
- Apparatus Function
- Appell Hypergeometric Function
- Appell Polynomial
- Appell Transformation
- Apple
- Approximately Equal
- Approximation Theory
- Apéry's Constant
- Arakelov Theory
- Arbelos
- Arborescence
- Arboricity
- Arc
- Arch
- Archimedean Solid
- Archimedean Solid Stellation
- Archimedean Spiral
- Archimedean Spiral Inverse Curve
- Archimedean Valuation
- Archimedes Algorithm
- Archimedes' Axiom
- Archimedes' Cattle Problem
- Archimedes' Circles
- Archimedes' Constant