Borromean rings
A three-components knot. The three threads are mutually untied (all the possible couples of components of the knot are untied), but the resulting knot isn't untied.
© matematita
immagine di Gian Marco Todesco
The image belongs to the sections...:
Three or more components knots (Topology)
Further information:
http://www.toonz.com/personal/todesco