anchor.diff:      static member singleton(framework,libs) =
           { Frameworks = Map.add framework libs Map.empty; Fallbacks = InstallFiles.empty }
   
  -    member this.ReplaceFramework(framework,f1,f2,f3) =
  +    member this.ReplaceFramework(framework,emptyReferencesF,mapReferencesF) =
           { this with Frameworks = 
                           match Map.tryFind framework this.Frameworks with
  -                        | Some files when Set.isEmpty files.References -> Map.add framework (f1()) this.Frameworks
  -                        | Some files -> Map.add framework (f2 files) this.Frameworks
  -                        | None -> 
  -                            match f3() with
  -                            | Some files -> Map.add framework files this.Frameworks
  -                            | None -> this.Frameworks }
  +                        | Some files when Set.isEmpty files.References |> not -> Map.add framework (mapReferencesF files) this.Frameworks
  +                        | _ -> Map.add framework (emptyReferencesF()) this.Frameworks }
   
   type InstallModel = 
       { PackageName : string
  
positive.code:                             group.ReplaceFramework(
                                  framework,
                                  (fun _ -> { References = newFiles; ContentFiles = Set.empty }),
                                  (fun files -> files),
                                  (fun _ -> Some({ References = newFiles; ContentFiles = Set.empty })))),
                          (fun _ -> Some(FrameworkGroup.singleton(framework,{ References = newFiles; ContentFiles = Set.empty }))))) this
      
      member this.UseLastInGroupAsFallback() = 
  
negative.code:                 group.ReplaceFramework(
                      framework,
                      (fun _ -> InstallFiles.singleton lib),
                      (fun files -> files.AddReference lib))),
              (fun _ -> Some(FrameworkGroup.singleton(framework,InstallFiles.singleton lib))))
  
      member this.AddReferences(libs, references) : InstallModel = 
  