anchor.diff:              callback evt world
           boxableCallback :> obj
   
  -    member internal this.Correlations 
  +    member private this.Correlations 
           with get () = correlations
   
       member this.GlobalSystem
  
positive.code:     member this.Components with get () = components
      member this.WithComponentsBuffered (fn : 'c ArrayRef -> 'w -> 'w) world = lock componentsBuffered (fun () -> fn componentsBuffered world)
  
      member this.Junctions with get () = junctions
      member this.WithJunctionsBuffered (fn : obj array -> 'w -> 'w) world = lock junctionsBuffered (fun () -> fn junctionsBuffered world)
  
      member internal this.Compact ecs =
  
          // compact array
          // TODO: P1: step-debug this.
  
negative.code:     let freeList = HashSet<int> HashIdentity.Structural
      let correlations = dictPlus<Guid, int> HashIdentity.Structural []
      let correlationsBack = dictPlus<int, Guid> HashIdentity.Structural []
      static member private isJunction<'c> junction = junction.GetType().GetElementType().GetGenericArguments().[0] = typeof<'c>
  
      new (ecs) = SystemCorrelated (typeof<'c>.Name, false, ecs)
      new (buffered, ecs) = SystemCorrelated (typeof<'c>.Name, buffered, ecs)
  