int ShiftFirst(IList<IList<int>> PostingLists, SplayTree<int> pqueue, int[] Start)
{
int pIndex = pqueue.RemoveFirst ();
var startIndex = Start[pIndex];
int docid = PostingLists[pIndex][startIndex];
startIndex++;
if (startIndex < PostingLists[pIndex].Count) {
Start[pIndex] = startIndex;
pqueue.Add (pIndex);
}
return docid;
}