Find the 2-link-connected components of
(2) Condense into a tree for which each node represents one of the 2-link-
    connected components of
(3) Number the nodes in in preorder, starting from an arbitrary non-leaf node
     /*PreOrder  */
(4) For choose links , where are the
     leaves of ordered in increasing node number
(5) Map the ends of each chosen link to an arbitrary node in the corresponding
    2-link-connected component
Algorithm 6: Eswaran-Tarjan-2-link-augmentation .