anchor.diff:  
                   pb.PutInt32 (prevPageNumber) // prev page num.
                   pb.PutInt16 (0) // number of pairs in this page. zero for now. written at end.
  -                // assert pb.Position is 8 (PAGE_OVERHEAD - sizeof(lastInt32))
  +                // assert pb.Position is 8 (LEAF_PAGE_OVERHEAD - sizeof(lastInt32))
               (*
                * one of the following cases must now be true:
                * 
  
positive.code:             let lastLeaf = fst nodelist.[nodelist.Count-1]
  
              let writeParentNodes (children:System.Collections.Generic.List<int32 * byte[]>) startingPageNumber startingBoundaryPageNumber =
                  let pageSize = pb.PageSize
                  let nextGeneration = new System.Collections.Generic.List<int32 * byte[]>()
                  let overflows = new System.Collections.Generic.Dictionary<int,int32>()
                  // TODO encapsulate mutables in a class?
  
negative.code:                 // 2 for the stored count
                  // 5 for the extra ptr we will add at the end, a varint, 5 is worst case
                  // 4 for lastInt32
                  let PARENT_PAGE_OVERHEAD = 2 + 2 + 5 + 4
  
                  let calcAvailable currentSize couldBeRoot =
                      let basicSize = pageSize - currentSize
  