anchor.diff:              (fun group -> 
                   group.ReplaceFramework(
                       framework,
  +                    (fun _ -> InstallFiles.singleton lib),
                       (fun files -> files.AddReference lib),
                       (fun _ -> Some (InstallFiles.singleton lib)))),
               (fun _ -> Some(FrameworkGroup.singleton(framework,InstallFiles.singleton lib))))
  
positive.code:                     model.AddOrReplaceGroup(
                          framework.Group,
                          (fun group ->
                              match Map.tryFind framework group.Frameworks with
                              | Some files when Set.isEmpty files.References -> 
                                  { group with Frameworks = 
                                                  Map.add framework { References = newFiles
                                                                      ContentFiles = Set.empty } 
                                                      group.Frameworks }
                              | None -> 
                                  { group with Frameworks = 
                                                  Map.add framework { References = newFiles
                                                                      ContentFiles = Set.empty } 
                                                      group.Frameworks }
                              | _ -> group),
                          (fun _ -> Some(FrameworkGroup.singleton(framework,{ References = newFiles; ContentFiles = Set.empty }))))) this
      
      member this.UseLastInGroupAsFallback() = 
  
negative.code:             (fun group ->
                  group.ReplaceFramework(
                      framework,
                      (fun _ -> InstallFiles.empty.AddFrameworkAssemblyReference assemblyName),
                      (fun files -> files.AddFrameworkAssemblyReference assemblyName),
                      (fun _ -> Some (InstallFiles.empty.AddFrameworkAssemblyReference assemblyName)))),
              (fun _ -> None))
  