$H(2)$-Unknotting Number of a Knot

An $H(2)$-move is a local move of a knot which is performed by adding ahalf-twisted band. It is known an $H(2)$-move is an unknotting operation. We definethe $H(2)$-unknotting number of a knot $K$ to be the minimum number of $H(2)$-movesneeded to transform K into a trivial knot. We give several methods to estimate the $H(2)$-unknotting number of a knot. Then we give tables of $H(2)$-unknotting numbersof knots with up to 9 crossings.