anchor.diff:                  group.ReplaceFramework(
                       framework,
                       (fun _ -> InstallFiles.empty.AddFrameworkAssemblyReference assemblyName),
  -                    (fun files -> files.AddFrameworkAssemblyReference assemblyName),
  -                    (fun _ -> Some (InstallFiles.empty.AddFrameworkAssemblyReference assemblyName)))),
  +                    (fun files -> files.AddFrameworkAssemblyReference assemblyName))),
               (fun _ -> None))
       
       member this.AddFrameworkAssemblyReferences(references) : InstallModel = 
  
positive.code:     static member singleton(framework,libs) =
          { Frameworks = Map.add framework libs Map.empty; Fallbacks = InstallFiles.empty }
  
      member this.ReplaceFramework(framework,f1,f2,f3) =
          { 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 }
  
  type InstallModel = 
      { PackageName : string
  
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 = 
  