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FIGUREEIGHT KNOT
The rope knot which, by connecting the two free blades, gives the mathematical figureeight knot is indeed shaped like an eight.  
However, the opposite knot is equivalent to the figureeight knot; therefore, it could also have been called "heart knot"! 

Here are, in order, the equations of the first 4 representations in the header:





Homemade representation based on a lemniscate of Gerono developed in space, the ends then being connected by a Bézier curve.
Cartesian parametrization: 
Paul
Bourke's representation, based on an epitrochoid with q = 2 and k = 5 .
Cartesian parametrization: 
Rohit Chaudhary's representation:  Representation based on a trochoid with d/R = 6, connected by an arch of ellipse.  Representation based on the cylindrical sine wave 
Opposite, drawings by G. K. Francis (a topological picture book) showing the passages between the various representations of the figureeight knot. 
The figureeight knot is one of the "Turk's heads".
See also the associated Seifert surface.
See more details on the website knot atlas.
Figureeight knot by Alain Esculier 
Figureeight knot on a stainedglass of the Chateau de Blois.

Mongolian frieze: infinite sum of figureeight knots (Batsukh Bold, Mongolian
national ornaments).
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© Robert FERRÉOL 2018