 Each node of the tree has a one-bit flag denoting "go left to find a pseudo-LRU element" or "go right to find a pseudo-LRU element".To find a pseudo-LRU element, traverse the tree according to the values of the flags.To update the tree with an access to an item N, traverse the tree to find N and, during the traversal, set the node flags to denote the direction that is opposite to the direction taken.