anchor.diff:              let system = Option.get systemOpt
               system.IndexUncorrelated index
   
  -        member this.RegisterUncorrelated<'c when 'c : struct and 'c :> 'c Component> ordered comp =
  +        member this.RegisterUncorrelated<'c when 'c : struct and 'c :> 'c Component> ordered comp (world : 'w) =
               match this.TryIndexSystem<'c, SystemUncorrelated<'c, 'w>> () with
  -            | Some system -> system.RegisterUncorrelated ordered comp
  -            | None -> failwith ("Could not find expected system '" + Unchecked.defaultof<'c>.TypeName + "'.")
  -
  -        member this.UnregisterUncorrelated<'c when 'c : struct and 'c :> 'c Component> index =
  +            | Some system -> system.RegisterUncorrelated ordered comp world
  +            | None -> failwith ("Could not find expected system '" + Unchecked.defaultof<'c>.TypeName + "'.")
  +
  +        member this.UnregisterUncorrelated<'c when 'c : struct and 'c :> 'c Component> index (world : 'w) =
               match this.TryIndexSystem<'c, SystemUncorrelated<'c, 'w>> () with
  -            | Some system -> system.UnregisterUncorrelated index
  +            | Some system -> system.UnregisterUncorrelated index world
               | None -> failwith ("Could not find expected system '" + Unchecked.defaultof<'c>.TypeName + "'.")
   
   /// An ECS system with components correlated by entity id (uint64).
  
positive.code:             | Some system -> system.IndexHierarchical entityId
              | None -> failwith ("Could not find expected system '" + Unchecked.defaultof<'c>.TypeName + "'.")
  
          member this.RegisterHierarchical<'c when 'c : struct and 'c :> 'c Component> ordered parentIdOpt comp entityId =
              match this.TryIndexSystem<'c, SystemHierarchical<'c, 'w>> () with
              | Some system -> system.RegisterHierarchical ordered parentIdOpt comp entityId
              | None -> failwith ("Could not find expected system '" + Unchecked.defaultof<'c>.TypeName + "'.")
  
          member this.UnregisterHierarchical<'c when 'c : struct and 'c :> 'c Component> parentIdOpt (world : 'w) =
  
negative.code:             let system = Option.get systemOpt
              system.IndexCorrelated entityId
  
          member this.RegisterCorrelated<'c when 'c : struct and 'c :> 'c Component> ordered comp entityId (world : 'w) =
              match this.TryIndexSystem<'c, SystemCorrelated<'c, 'w>> () with
              | Some system -> system.RegisterCorrelated ordered comp entityId world
              | None -> failwith ("Could not find expected system '" + Unchecked.defaultof<'c>.TypeName + "'.")
  
          member this.UnregisterCorrelated<'c when 'c : struct and 'c :> 'c Component> entityId (world : 'w) =
              match this.TryIndexSystem<'c, SystemCorrelated<'c, 'w>> () with
              | Some system -> system.UnregisterCorrelated entityId world
              | None -> failwith ("Could not find expected system '" + Unchecked.defaultof<'c>.TypeName + "'.")
  
  /// A SystemHierarchical node.
  type [<NoEquality; NoComparison>] NodeHierarchical<'c when 'c : struct and 'c :> 'c Component> =
  