anchor.diff:  
   [<Test>]
   let ``flat is equivalent to List.concat``() =
  -    assertProp "flat" <| fun xss ->
  +    assertProp "flat" <| fun (xss : string list list) ->
           flat xss = List.concat xss
   
   [<Test>]
  
positive.code: 
  [<Test>]
  let ``end_itlist is equivalent to List.reduceBack on non-empty lists``() =
      assertProp "end_itlist" <| fun (xs : int list) f ->
          xs <> [] ==> lazy (end_itlist f xs = List.reduceBack f xs)
  
  [<Test>]
  
negative.code: 
  // The `lazy` keyword is important in order to avoid early evaluation
  [<Test>]
  let ``find is equivalent to List.tryFind``() =
      assertProp "find" <| fun xs ->
          List.exists (fun x -> x > 0) xs ==>
              lazy (find (fun x -> x > 0) xs = List.tryFind (fun x -> x > 0) xs)
  
  [<Test>]
  let ``index is equivalent to List.findIndex``() =
  