anchor.diff:              .UseLowerVersionLibForSpecicalFrameworksIfEmpty()
               .FilterBlackList()
               .UseLastInGroupAsFallback()
  +            .UseLastGroupFallBackAsDefaultFallBack()
   
       member this.BuildModel() = this.BuildUnfilteredModel().DeleteIfGroupFallback()
       
  
positive.code:             match newGroupF() with
              | Some newGroup -> { this with Groups = Map.add groupId newGroup this.Groups }
              | None -> this
          
  
      member this.AddReference(framework : FrameworkIdentifier, lib : string, references) : InstallModel = 
  
negative.code:                 | Reference.Library lib -> not (lib.EndsWith ".dll" || lib.EndsWith ".exe")
                  | _ -> false ]
  
          this.MapGroups(fun _ group -> 
                                 { group with Frameworks = 
                                                  blackList 
                                                  |> List.fold 
  