anchor.diff:  
                       snapshot <-
                           use edit = subjectBuffer.CreateEdit()
  +
  +                        edit.Insert(closingSnapshotPoint.Position, closingBrace.ToString()) |> ignore
                       
                           if edit.HasFailedChanges then
                               Debug.Fail("Unable to insert closing brace")
  
positive.code: open System.Diagnostics
  open System.Runtime.InteropServices
  open System.Composition
  open Microsoft.CodeAnalysis.Host.Mef
  open Microsoft.VisualStudio.Utilities
  
  
negative.code:                                 editorOperationsFactoryService, 
                                  editorSession) :> IBraceCompletionSession
  
              session <- newSession
  
              match session with
              | null -> false
              | _ -> true