for tree operations (insertion and removal of nodes and edges) and
poly-logarithmic time for nearest common ancestor.
- ET tree strores its structue as a sequence of symbols obtained
+ ET tree stores its structure as a sequence of symbols obtained
by dfs(root)
dfs (node)
the sequence is 1 2 4 2 5 3 1 3 1 4 1.
- The sequence is stored in a sligtly modified splay tree.
+ The sequence is stored in a slightly modified splay tree.
In order to support various types of node values, a hashtable
is used to convert node values to the internal representation. */