Abstract
A circle embedded in 3-space without self-intersection is called a knot. A knot is a mathematical object according to topology. Knot theory studies how complicated a given knot is, or whether it is trivial. Any knot can be represented by a diagram with above and below information at the crossings. Then a knot obtained by replacing the information at one crossing is generally another knot. This operation is called a crossing change. A crossing change is an important notion in knot theory. In this article, we survey the strong triviality of knots, which is one of the multi-crossing changes.
