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Definition:
A knot is a simple closed curve in 3-dimensional space.
What does that mean? Well, a loop like the one at the left is considered a knot in mathematical knot theory (it is a simple closed curve in 3-dimensional space). In fact this knot has a special name: The unknot. The unknot can be drawn with no crossings, and is also called a trivial knot. It is the simplest of all knots.
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The Borromean knot
So called because the figure is found on the coat of arms of the Borromeo family, the Borromean Knot is a group of three rings which are linked in such a way that if any one of them is cut, all three become separated. In his late seminars, i.e., from Seminar XX onwards, Lacan uses the Borromean knot as a way of illustrating the interdependence of the three orders of the real, the symbolic and the imaginary. This corresponds to a rethinking of the relationship between language and the body in the structuring of the subject.