**Topology** is a fascinating branch of mathematics that describes the properties of an object that remain unchanged under continuous “smooth” deformations. Actually, many 3D puzzles are based on topological principles and understanding some very basic principles may help you analyze whether a puzzle is possible or not.

Puzzle-Meister **G. Sarcone** created this amusing everyday-life topological puzzle to help children to easily take their shoes off.

As you know, the standard shoelace knot is designed for quick release and easily comes untied when either of the working ends is pulled. Thus, most people think that tying a shoelace into a double knot is an effective method of making the knot “permanent”. **But is it true?** Continue reading “How to ‘magically’ untie a shoelace double knot”