anchor.diff:  
           [<CompiledName("Average")>]
           let inline average      (list:list<'T>) =
  -            checkNonNull "list" list
               match list with 
               | [] -> invalidArg "source" LanguagePrimitives.ErrorStrings.InputSequenceEmptyString;
               | _ ->
  
positive.code:                 loop list LanguagePrimitives.GenericZero< 'T > 0
  
          [<CompiledName("AverageBy")>]
          let inline averageBy f (list:list<_>) = Seq.averageBy f list
  
          [<CompiledName("Collect")>]
          let collect f list = Microsoft.FSharp.Primitives.Basics.List.collect f list
  
negative.code:     module List = 
  
          let inline indexNotFound() = raise (new System.Collections.Generic.KeyNotFoundException(SR.GetString(SR.keyNotFoundAlt)))
  
          [<CompiledName("Length")>]
          let length (list: 'T list) = list.Length
  