Borromean rings  

L6a4  
Braid length  6 
Braid no.  3 
Crossing no.  6 
Hyperbolic volume  7.327724753 
Stick no.  9 
Unknotting no.  2 
Conway notation  [.1] 
AB notation  6^{3} _{2} 
Thistlethwaite  L6a4 
Last /Next  L6a3 / L6a5 
Other  
alternating, hyperbolic 
In mathematics, the Borromean rings consist of three topological circles which are linked but where removing any one ring leaves the other two unconnected. In other words, no two of the three rings are linked with each other as a Hopf link, but nonetheless all three are linked. The Borromean rings are one of a class of such links called Brunnian links.
Unsolved problem in mathematics: Are there three unknotted curves, not all circles, that cannot form the Borromean rings? (more unsolved problems in mathematics)

The Borromean rings are typically drawn with their rings projecting to circles in the plane of the drawing, but threedimensional circular Borromean rings are an impossible object: it is not possible to form the Borromean rings from circles in threedimensional space.^{[1]}Michael H. Freedman and Richard Skora (1987) proved that a certain class of links, including the Borromean links, cannot be exactly circular.^{[2]} For three rings in their conventional Borromean arrangement, this can be seen from considering the link diagram. If one assumes that two of the circles touch at their two crossing points, then they lie in either a plane or a sphere. In either case, the third circle must pass through this plane or sphere four times, without lying in it, which is impossible.^{[3]}
However, the Borromean rings can be realized using ellipses.^{[4]} These may be taken to be of arbitrarily small eccentricity; i.e. no matter how close to being circular their shape may be, as long as they are not perfectly circular, they can form Borromean links if suitably positioned.
A realization of the Borromean rings by three mutually perpendicular golden rectangles can be found within a regular icosahedron by connecting three opposite pairs of its edges.^{[4]}
Every three unknotted polygons in Euclidean space may be combined, after a suitable scaling transformation, to form the Borromean rings. If all three polygons are planar, then scaling is not needed. More generally, Matthew Cook has conjectured that any three unknotted simple closed curves in space, not all circles, can be combined without scaling to form the Borromean rings. After Jason Cantarella suggested a possible counterexample, Hugh Nelson Howards weakened the conjecture to apply to any three planar curves that are not all circles. On the other hand, although there are infinitely many Brunnian links with three links, the Borromean rings are the only one that can be formed from three convex curves.^{[5]}
In knot theory, the Borromean rings are a simple example of a Brunnian link: although each pair of rings is unlinked, the whole link cannot be unlinked. There are a number of ways of seeing that the Borromean rings are linked; one is to count their Fox ncolorings. A trivial link would have 125 Fox 5colorings (one for each choice of color for each of the three links), but the Borromean rings have only five.^{[1]}
In arithmetic topology, there is an analogy between knots and prime numbers in which one considers links between primes. The triple of primes are linked modulo 2 (the Rédei symbol is 1) but are pairwise unlinked modulo 2 (the Legendre symbols are all 1). Therefore, these primes have been called a "proper Borromean triple modulo 2"^{[6]} or "mod 2 Borromean primes".^{[7]}
The Borromean rings are a hyperbolic link: the complement of the Borromean rings in the 3sphere admits a complete hyperbolic metric of finite volume. The canonical (EpsteinPenner) polyhedral decomposition of the complement consists of two ideal regular octahedra. The volume is where is the Lobachevsky function.^{[8]} This was a central example in the video Not Knot about knot complements, produced in 1991 by the Geometry Center.^{[9]}
The name "Borromean rings" comes from their use in the coat of arms of the aristocratic Borromeo family in Northern Italy.^{[10]} The link itself is much older and has appeared in the form of the valknut, three linked equilateral triangles with parallel sides, on Norse image stones dating back to the 7th century.^{[11]} A stone pillar in the 6thcentury Marundeeswarar Temple in India shows the Borromean rings in another form, three linked equilateral triangles rotated from each other to form a regular enneagram.^{[12]} The ?miwa Shrine in Japan is also decorated with a motif of the Borromean rings, in their conventional circular form.^{[4]}
The Borromean rings have been used in different contexts to indicate strength in unity.^{[13]} In particular, some have used the design to symbolize the Trinity.^{[14]} The psychoanalyst Jacques Lacan found inspiration in the Borromean rings as a model for his topology of human subjectivity, with each ring representing a fundamental Lacanian component of reality (the "real", the "imaginary", and the "symbolic").^{[15]}
The rings were used as the logo of Ballantine beer, and are still used by the Ballantine brand beer, now distributed by the current brand owner, the Pabst Brewing Company.^{[16]}^{[17]} For this reason they have sometimes been called the "Ballantine rings".^{[14]}^{[16]}
Seifert surfaces for the Borromean rings were featured by Martin Gardner in his September 1961 "Mathematical Games column" in Scientific American.^{[17]} In 2006, the International Mathematical Union decided at the 25th International Congress of Mathematicians in Madrid, Spain to use a new logo based on the Borromean rings.^{[4]}
In medieval and renaissance Europe, a number of visual signs are found that consist of three elements interlaced together in the same way that the Borromean rings are shown interlaced (in their conventional twodimensional depiction), but the individual elements are not closed loops. Examples of such symbols are the Snoldelev stone horns^{[18]} and the Diana of Poitiers crescents.^{[14]}
Similarly, a monkey's fist knot is essentially a 3dimensional representation of the Borromean rings, albeit with three layers, in most cases.^{[19]} Using the pattern in the incomplete Borromean rings, one can balance three knives on three supports, such as three bottles or glasses, providing a support in the middle for a fourth bottle or glass.^{[20]}
Some knottheoretic links contain multiple Borromean rings configurations; one fiveloop link of this type is used as a symbol in Discordianism, based on a depiction in the Principia Discordia.^{[21]}
Molecular Borromean rings are the molecular counterparts of Borromean rings, which are mechanicallyinterlocked molecular architectures. In 1997, biologist Chengde Mao and coworkers of New York University succeeded in constructing a set of rings from DNA.^{[23]} In 2003, chemist Fraser Stoddart and coworkers at UCLA utilised coordination chemistry to construct a set of rings in one step from 18 components.^{[22]} Borromean ring structures have been shown to be an effective way to represent the structure of certain atomically precise noble metal clusters which are shielded by a surface layer of thiolate ligands (SR), such as Au_{25}(SR)_{18} and Ag_{25}(SR)_{18}.^{[24]} A library of Borromean networks has been synthesized by design by Giuseppe Resnati and coworkers via halogen bond driven selfassembly.^{[25]} In order to access the molecular Borromean ring consisting of three unequal cycles a stepbystep synthesis was proposed by Jay S. Siegel and coworkers.^{[26]}
A quantummechanical analog of Borromean rings is called a halo state or an Efimov state (the existence of such states was predicted by physicist Vitaly Efimov, in 1970). For the first time the research group of Rudolf Grimm and HannsChristoph Nägerl from the Institute for Experimental Physics (University of Innsbruck, Austria) experimentally confirmed such a state in an ultracold gas of caesium atoms in 2006, and published their findings in the scientific journal Nature.^{[27]} A team of physicists led by Randall Hulet of Rice University in Houston achieved this with a set of three bound lithium atoms and published their findings in the online journal Science Express.^{[28]} In 2010, a team led by K. Tanaka created an Efimov state within a nucleus.^{[29]}
they represent the motto 'united we stand, divided we fall', since if one of the rings is cut the other two fall apart
the stone bears also representations of three horns interlaced