Realizing Exterior Cromwell moves on rectangular diagrams by   Reidemeister moves
  If a rectangular diagram represents the trivial knot, then it can be deformed into the trivial rectangular diagram with only four edges by a finite sequence of merge operations and exchange operations, without increasing the number of edges, which was shown by I. A. Dynnikov.   Using this, Henrich and Kauffman gave an upper bound for the number of Reidemeister moves needed for unknotting a knot diagram of the trivial knot.   However, exchange or merge moves on the top and bottom pairs of edges of rectangular diagrams are not considered in the proof.   In this paper, we show that there is a rectangular diagram of the trivial knot which needs such an exchange move for being unknotted, and study upper bound of the number of Reidemeister moves needed for realizing such an exchange or merge move. 
Tatsuo Ando, Chuichiro Hayashi, Yuki Nishikawa
math.GT