anchor.diff:          fieldSpace.ContainsProp
       
       member this.ContainsPickup =
  -        match this.PickupItemOpt with Some _ -> true | None -> false
  +        match this.PickupOpt with Some _ -> true | None -> false
       
       static member containsPickup (fieldSpace : FieldSpace) =
           fieldSpace.ContainsPickup
  
positive.code:             | Some prop -> Some (OccupyingProp prop)
              | None -> None
      
      member this.GetPickupItem =
          match this.PickupItemOpt with Some pickup -> pickup | None -> failwithumf ()
      
      member this.ContainsCharacter =
          match this.CharacterOpt with Some _ -> true | None -> false
  
negative.code:     static member updatePropOpt updater fieldSpace =
          { fieldSpace with PropOpt = updater fieldSpace.PropOpt }
      
      static member updatePickupOpt updater fieldSpace =
          { fieldSpace with PickupOpt = updater fieldSpace.PickupOpt }
      
      static member updateCharacterInternal updater characterOpt =
          match characterOpt with
  