code: function mergeLeaves(edit, shift, h1, n1, h2, n2) {
      if (h1 === h2) return Collision(edit, h1, [n2, n1]);
  
      var subH1 = hashFragment(shift, h1);
      var subH2 = hashFragment(shift, h2);
      return IndexedNode(edit, toBitmap(subH1) | toBitmap(subH2), subH1 === subH2 ? [mergeLeaves(edit, shift + SIZE, h1, n1, h2, n2)] : subH1 < subH2 ? [n1, n2] : [n2, n1]);
  }
docs: Merge two leaf nodes.
  
  @param shift Current shift.
  @param h1 Node 1 hash.
  @param n1 Node 1.
  @param h2 Node 2 hash.
  @param n2 Node 2.