Borromeo-Ringe
"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.
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Although the typical picture of the Borromean rings may lead one to think the link can be formed from geometrically ideal circular rings, they cannot be."
https://en.wikipedia.org/wiki/Borromean_rings
Visualisierung mit GeoGebra: Hans-Jürgen Elschenbroich
Zoom mit rechter Maustaste.