anchor.diff:          let index = this.GetComponentIndex entityId
           &components.[index]
   
  -    abstract member Register : Guid -> 'w Ecs -> int
  -    default this.Register entityId _ =
  +    member this.GetEntities () =
  +        correlations.Keys :> _ IEnumerable
  +
  +    abstract member RegisterEntity : Guid -> 'w Ecs -> int
  +    default this.RegisterEntity entityId _ =
           match Dictionary.tryGetValue entityId correlations with
           | (false, _) ->
               let comp = Unchecked.defaultof<'t>
  
positive.code:         (entityId : Guid)
          (ecs : 'w Ecs) =
          let system = junctions.[typeof<'t>.Name] :?> SystemCorrelated<'t, 'w>
          let index = system.Register entityId ecs
          ComponentRef.make index system.Components
  
      let disjunction<'t, 'w when 't : struct and 't :> Component>
  
negative.code:             comp.RefCount <- inc comp.RefCount
              index
  
      abstract member UnregisterEntity : Guid -> 'w Ecs -> bool
      default this.UnregisterEntity entityId _ =
          match correlations.TryGetValue entityId with
          | (true, index) ->
              if index <> freeIndex then
  