anchor.diff:                  fun (xs: int list) ->
                       List.sort (List.ofSeq (Seq.distinct xs)) = [ for (x,()) in IntMap.toList (IntMap.ofList [ for x in xs do yield (x,()) ]) do yield x ]
   
  -            ptestPropertyWithConfig config10k "prop alter" <|
  +            testPropertyWithConfig config10k "prop alter" <|
                   fun t k ->
                       let f = function | Some () -> None | None -> Some ()
                       let t' = IntMap.alter f k t
  
positive.code:             testPropertyWithConfig config10k "prop insert and tryFind" <|
                  fun k t -> IntMap.tryFind k (IntMap.insert k () t) <> None
  
              ptestPropertyWithConfig config10k "prop insert and delete" <|
                  fun k t -> IntMap.tryFind k t = None ==> (IntMap.delete k (IntMap.insert k () t) = t)
  
              ptestPropertyWithConfig config10k "prop delete non member" <|
                  fun k t -> IntMap.tryFind k t = None ==> (IntMap.delete k t = t)
  
              testPropertyWithConfig config10k "prop append" <|
  
negative.code: 
  module IntMapTest =
      type IntMapGen =
          static member IntMap() = Arb.generate |> Gen.listOf |> Gen.map IntMap.ofSeq  |> Arb.fromGen
  
  
      let testPropertyWithConfig config = testPropertyWithConfig {config with arbitrary = typeof<IntMapGen> :: config.arbitrary}
  
      [<Tests>]
      let testIntMap =
  