Question 4
==========

Reading undocumented code is challenging.
What is the meaning of XYZ.xyz(Object o)?
Explain in English what the method computes.
Give a precondition and a post-condition
that captures the meaning of the method.

class XYZ extends IDba{
    int update(NodeInt n, int i){ return i+1; }
    int combine(NodeInt t, int d, int l, int r){ return Math.max(l,r); }
    int combine(Object n, int i){ return i; }
    int combine(BSTInt n, int i){ return i; }

    static int xyz (Object o)
    {
	return new Traversal(new XYZ()). <Integer> traverse(o,0);
    }
}