Editing Splay tree (section)

=== Split ===
Given a tree and an element ''x'', return two new trees: one containing all elements less than or equal to ''x'' and the other containing all elements greater than ''x''. This can be done in the following way:
* Splay ''x''. Now it is in the root so the tree to its left contains all elements smaller than ''x'' and the tree to its right contains all element larger than ''x''. 
* Split the right subtree from the rest of the tree.