anchor.diff:              let mutable c = 0
               for i in appendMap do
                 c <- c + 1
  -              this.AddLast(i.Key, i.Value) // TODO Add last when fixed flushing
  +              this.AddUnchecked(i.Key, i.Value) // TODO Add last when fixed flushing
               c
           | AppendOption.IgnoreEqualOverlap ->
             if this.IsEmpty || comparer.Compare(appendMap.First.Key, this.Last.Key) > 0 then
               let mutable c = 0
               for i in appendMap do
                 c <- c + 1
  -              this.AddLast(i.Key, i.Value) // TODO Add last when fixed flushing
  +              this.AddUnchecked(i.Key, i.Value) // TODO Add last when fixed flushing
               c
             else
               let isEqOverlap = hasEqOverlap this appendMap
               if isEqOverlap then
                 let appC = appendMap.GetCursor();
                 if appC.MoveAt(this.Last.Key, Lookup.GT) then
  -                this.AddLast(appC.CurrentKey, appC.CurrentValue) // TODO Add last when fixed flushing
  +                this.AddUnchecked(appC.CurrentKey, appC.CurrentValue) // TODO Add last when fixed flushing
                   let mutable c = 1
                   while appC.MoveNext() do
  -                  this.AddLast(appC.CurrentKey, appC.CurrentValue) // TODO Add last when fixed flushing
  +                  this.AddUnchecked(appC.CurrentKey, appC.CurrentValue) // TODO Add last when fixed flushing
                     c <- c + 1
                   c
                 else 0
  
positive.code:             let mutable c = 0
              for i in appendMap do
                c <- c + 1
                this.AddLast(i.Key, i.Value) // TODO Add last when fixed flushing
              c
            else
              let removed = this.RemoveMany(appendMap.First.Key, Lookup.GE)
  
negative.code:             let mutable c = 0
              for i in appendMap do
                c <- c + 1
                this.AddUnchecked(i.Key, i.Value) // TODO Add last when fixed flushing
              c
            else 
              let exn = SpreadsException("values overlap with existing")
  