anchor.diff:        
         let c = 
           if outerMap.IsEmpty then -1
  -        else comparer.Compare(key, this.First.Key)
  +        else comparer.Compare(key, this.FirstUnsafe.Key)
         if c < 0 then 
           this.AddUnchecked(key, value)
         else 
  -        let exn = OutOfOrderKeyException(this.Last.Key, key, "New key is larger or equal to the smallest existing key")
  +        let exn = OutOfOrderKeyException(this.LastUnsafe.Key, key, "New key is larger or equal to the smallest existing key")
           raise (exn)
       finally
         Interlocked.Increment(&this.version) |> ignore
         exitWriteLockIf &this.locker entered
         #if PRERELEASE
  +      Trace.Assert(outerMap.Version = this.version)
         if entered && this.version <> this.nextVersion then raise (ApplicationException("this.orderVersion <> this.nextVersion"))
         #else
         if entered && this.version <> this.nextVersion then Environment.FailFast("this.orderVersion <> this.nextVersion")
  
positive.code:             let isEqOverlap = hasEqOverlap this appendMap
              if isEqOverlap then
                let appC = appendMap.GetCursor();
                if appC.MoveAt(this.Last.Key, Lookup.GT) then
                  this.AddUnchecked(appC.CurrentKey, appC.CurrentValue) // TODO Add last when fixed flushing
                  let mutable c = 1
                  while appC.MoveNext() do
  
negative.code:       removed
      finally
        if removed && this.subscribersCounter > 0 then this.onUpdateEvent.Trigger(false)
        if removed then Interlocked.Increment(&this.version) |> ignore
        else Interlocked.Decrement(&this.nextVersion) |> ignore
        exitWriteLockIf &this.locker entered
        #if PRERELEASE
        Trace.Assert(outerMap.Version = this.version)
        if entered && this.version <> this.nextVersion then raise (ApplicationException("this.orderVersion <> this.nextVersion"))
        #else
        if entered && this.version <> this.nextVersion then Environment.FailFast("this.orderVersion <> this.nextVersion")
  