anchor.diff:      let add x (call : DrawCallInfo) =
           locked x (fun () ->
               if indices.ContainsKey call then 
  -                false
  +                false // THIS SHOULD NEVER HAPPEN
               else
                   let index = calls.Count
                   indices.[call] <- calls.Count
  
positive.code:                         
                      true
                  | _ ->
                      false
          )
  
      member x.Add (call : DrawCallInfo) =
  
negative.code:             
              let pool = p.Pool
              
              let additions = new List<DrawCallInfo>()
              let removals = new List<DrawCallInfo>()
  
              let r = (p.Calls |> ASet.map (fun mdc -> mdc.Call)).GetReader()
              let calls =
                  let buffer = DrawCallBuffer(pool.Runtime, true) // who manages this? using finalizer for now
  