Unknotting number

In the mathematical area of knot theory, the unknotting number of a knot is the minimum number of times the knot must be passed through itself (crossing switch) to untie it.

, then there exists a diagram of the knot which can be changed to unknot by switching

[2] This invariant was first defined by Hilmar Wendt in 1936.

The following table show the unknotting numbers for the first few knots: In general, it is relatively difficult to determine the unknotting number of a given knot.

Known cases include: This knot theory-related article is a stub.

Trefoil knot without 3-fold symmetry being unknotted by one crossing switch.
Whitehead link being unknotted by undoing one crossing