Figure 3: Example of mirror torus QS: and initiate their tail selection in a backward manner; that is, the first element of node A is selected from column (a mirror of ), and the one of node is selected from column (a mirror of ). Then, both nodes select the next tail element in a forward manner, thus from column, which is in case of node , and in case of node B. The third tail element is selected in a backward manner, which is in case of node , and in case of node . The last element of nodes and falls in the same (mirror) column. Nodes meet at slot 5 (they would meet in one element of column anyway) and additionally in slot 18. Hence, nodes can always alternate the manner, either forward or backward, while picking up elements; however, they need to have the same , in this example , where .