anchor.diff:  
               // new component; use a pre-allocated component
               if preDeque.Count > 0 then
  -                let index = preDeque.RemoveFromFront ()
  +                let index = Seq.head preDeque
  +                let _ : bool = preDeque.Remove index
                   correlations.Add (entityId, index)
                   components.Array.[index] <- comp
                   let comp = &components.Array.[index]
  
positive.code:                         comp.RefCount <- inc comp.RefCount
                          components.Array.[index] <- comp
                          correlations.Add (entityId, index)
                      else
                          preDeque.AddToBack index
  
                  // fin
                  entityId
  
negative.code:     let mutable components = ArrayRef<'c>.make reserve
      let mutable freeIndex = 0
      let freeList = HashSet<int> ()
      let preDeque = HashSet<int> ()
      let correlations = dictPlus [] : Dictionary<Guid, int>
  
      new (reserve) = SystemCorrelated (reserve, typeof<'c>.Name)
  