anchor.diff:          for storeEntry in stores do
               comps.Add (storeEntry.Key, storeEntry.Value.[index])
           comps
  +
  +    member this.Read count (stream : FileStream) =
  +        for storeEntry in stores do
  +            let store = storeEntry.Value
  +            store.Read count freeIndex stream
  +        freeIndex <- freeIndex + count
   
   type [<StructuralEquality; NoComparison>] 'w SystemSlot =
       { SystemIndex : int
  
positive.code: open System.Collections.Generic
  open Prime
  open Nu
  
  type SystemId = string HashSet
  
  
negative.code:             if query.CheckCompatibility system then
                  query.RegisterSystem system
          system
  
      member this.ReadComponents count systemId stream =
          match systems.TryGetValue systemId with
          | (true, system) -> system.Read count stream
          | (false, _) -> failwith "Could not find system."
  
      member private this.RegisterNamedComponentInternal<'c when 'c : struct and 'c :> 'c Component> (comp : 'c) compName entityId world =
          match systemSlots.TryGetValue entityId with
  