Similarly, the unknot is the identity element with respect to the knot sum operation.

While rope is generally not in the form of a closed loop, sometimes there is a canonical way to imagine the ends being joined together.

From this point of view, many useful practical knots are actually the unknot, including those that can be tied in a bight.

[1] Every tame knot can be represented as a linkage, which is a collection of rigid line segments connected by universal joints at their endpoints.

[2] Like crossing number, a linkage might need to be made more complex by subdividing its segments before it can be simplified.