template <class T> class VL_SkipList{
	protected:
		VL_SkipListEntry<T>* head;
		int size;
		unsigned int maxlevel;
		unsigned int prob_denominator;
		int pow_maxlevel;
				
	public:
		VL_SkipList(unsigned int prob_denom = 2){
			head = new VL_SkipListEntry<T>(0,maxlevel,NULL);
			maxlevel = 8;
			prob_denominator = 100/prob_denom;
			pow_maxlevel = (int)pow(2,maxlevel);
			size = 1;
		}
....
---

template <class T> class VL_2DSkipList : public VL_SkipList<VL_SkipList<T>*> {
	public:
		VL_2DSkipList(unsigned int prob_denom = 2) 
			: VL_SkipList<VL_SkipList<T>*>(prob_denom){

			// head undeclared ??
                        head->add_data(new VL_SkipList<T>(prob_denom));
		}
...