anchor.diff:  ﻿namespace MBrace.AWS.Runtime
   
   open System
  -open System.Collections.Generic
  +open System.Collections.Concurrent
   open System.Runtime.Serialization
   
   open MBrace.Core.Internals
  
positive.code:         member x.UUID: string = uuid
  
          member x.Cancel(): Async<unit> = async {
              let visited = new HashSet<string>()
              let rec walk id = async {
                  if not <| visited.Contains id then
                      let! e = getTable().UpdateItemAsync(TableKey.Hash id, cancelOp, returnLatest = false)
                      if e.IsCancellationRequested then ()
                      else
                          let _ = visited.Add id
                          do! e.Children' |> Seq.map walk |> Async.Parallel |> Async.Ignore
              }
  
  
negative.code:     let private template = RecordTemplate.Define<CancellationEntry>()
  
      let isNotCancelled = template.PrecomputeConditionalExpr <@ fun c -> c.IsCancellationRequested = false @>
      let cancelOp = template.PrecomputeUpdateExpr <@ fun c -> { c with IsCancellationRequested = true } @>
      let addChild = template.PrecomputeUpdateExpr <@ fun ch c -> { c with Children = ch :: c.Children } @>
  
  [<Sealed; DataContract>]
  