anchor.diff:  
       [<CompiledName("FoldBack")>]
       let foldBack<'Key, 'T, 'State  when 'Key : comparison> folder (table: Map<'Key, 'T>) (state:'State) =
  -        MapTree.foldBack  folder table.Tree state
  +        MapTree.foldBack folder table.Tree state
   
       [<CompiledName("ToSeq")>]
       let toSeq (table: Map<_, _>) =
  
positive.code: 
      [<CompiledName("FindKey")>]
      let findKey predicate (table : Map<_, _>) =
          table |> toSeq |> Seq.pick (fun (k, v) -> if predicate k v then Some k else None)
  
      [<CompiledName("TryFindKey")>]
      let tryFindKey predicate (table : Map<_, _>) =
          table |> toSeq |> Seq.tryPick (fun (k, v) -> if predicate k v then Some k else None)
  
      [<CompiledName("OfList")>]
      let ofList (elements: ('Key * 'Value) list) =
  
negative.code:     member __.OnDeserialized(context: System.Runtime.Serialization.StreamingContext) =
          ignore context
          comparer <- LanguagePrimitives.FastGenericComparer<'Key>
          tree <- serializedData |> Array.map (fun kvp -> kvp.Key, kvp.Value) |> MapTree.ofArray comparer
          serializedData <- null
  
      static member Empty : Map<'Key, 'Value> =
  