On knots having zero negative unknotting number Yuanyuan Bao 57M2757M25negative unknotting numberDehn surgeryOzsv{\\\'a}th and Szab{\\\'o}\'s $d$-invariant A knot in the 3-sphere is said to have zero negative unknotting number if it can be transformed into the unknot by performing only positive crossing changes. In this paper, we provide an obstruction to a knot's having zero negative unknotting number, and discuss its application to two classes of knots. Indiana University Mathematics Journal 2014 text pdf 10.1512/iumj.2014.63.5223 10.1512/iumj.2014.63.5223 en Indiana Univ. Math. J. 63 (2014) 597 - 613 state-of-the-art mathematics http://iumj.org/access/