anchor.diff:              pb.Flush(fs)
               if nextPageNumber <> (thisPageNumber+1) then utils.SeekPage(fs, pb.PageSize, nextPageNumber)
               nodelist.Add(thisPageNumber, lastKey)
  +
  +        // all the leaves are written.
  +        // now write the parent pages.
  +        // maybe more than one level of them.
  +        // keep writing until we have written a level which has only one node,
  +        // which is the root node.
           if nodelist.Count > 0 then
               let firstLeaf = fst nodelist.[0]
               let lastLeaf = fst nodelist.[nodelist.Count-1]
  -            // now write the parent pages.
  -            // maybe more than one level of them.
  -            // keep writing until we have written a level which has only one node,
  -            // which is the root node.
               while nodelist.Count > 1 do
                   let (newNextPageNumber,newBoundaryPageNumber,newNodelist) = writeParentNodes pageManager token firstLeaf lastLeaf nodelist nextPageNumber boundaryPageNumber fs pb pbOverflow
                   nextPageNumber <- newNextPageNumber
  
positive.code:                 pb.PutInt32(valueOverflowFirstPage)
              lastKey <- k
              countPairs <- countPairs + 1
          if pb.Position > 0 then
              // note similar flush code above
              let thisPageNumber = nextPageNumber
  
negative.code:                     // another page.
                      if thisPageNumber = boundaryPageNumber then
                          pb.SetPageFlag FLAG_BOUNDARY_NODE
                          let (nextPage,boundaryPage) = pageManager.GetRange(token)
                          // assert pb.Position <= (pb.PageSize - 4)
                          pb.SetLastInt32(nextPage)
                          nextPageNumber <- nextPage
                          boundaryPageNumber <- boundaryPage
                      else
                          nextPageNumber <- nextPageNumber + 1
                      pb.PutInt16At (OFFSET_COUNT_PAIRS, countPairs)
  