anchor.diff:      member this.PickupCount =
           this.PickupSpaces.Count
       
  -    
  -    
  -    static member updateFieldSpaces updater chessboard =
  -        { chessboard with FieldSpaces = updater chessboard.FieldSpaces }
  -    
  -    static member characterExists index chessboard =
  -        Map.exists (fun _ v -> FieldSpace.containsSpecifiedCharacter index v) chessboard.FieldSpaces
  -    
  -    static member pickupAtCoordinates coordinates chessboard =
  -        chessboard.FieldSpaces.[coordinates].ContainsPickup
  -    
  -    static member updateByCoordinatesInternal coordinates updater (fieldSpaces : Map<Vector2i, FieldSpace>) =
  -        Map.add coordinates (updater fieldSpaces.[coordinates]) fieldSpaces
  -
  -    static member updateByPredicateInternal predicate updater (fieldSpaces : Map<Vector2i, FieldSpace>) =
  -        Map.map (fun _ v -> if predicate v then updater v else v) fieldSpaces
  -    
  -    static member updateByCoordinates coordinates updater chessboard =
  -        Chessboard.updateFieldSpaces (Chessboard.updateByCoordinatesInternal coordinates updater) chessboard
  -    
  -    static member updateByPredicate predicate updater chessboard =
  -        Chessboard.updateFieldSpaces (Chessboard.updateByPredicateInternal predicate updater) chessboard
  -    
  -    static member addHealth _ coordinates chessboard =
  -        Chessboard.updateByCoordinates coordinates (FieldSpace.addPickup Health) chessboard
  -
  -    static member removePickup _ coordinates chessboard =
  -        Chessboard.updateByCoordinates coordinates FieldSpace.removePickup chessboard
  -    
  -    static member clearPickups _ _ chessboard =
  -        Chessboard.updateByPredicate FieldSpace.containsPickup FieldSpace.removePickup chessboard
  -    
       static member getCharacterCoordinates index chessboard =
           Map.findKey (fun _ v -> FieldSpace.containsSpecifiedCharacter index v) chessboard.FieldSpaces
   
  
positive.code:         let coordinates = Chessboard.getCharacterCoordinates index chessboard
          Chessboard.updateByCoordinates coordinates (FieldSpace.updateCharacter updater) chessboard
      
      static member removeCharacter index _ chessboard =
          let coordinates = Chessboard.getCharacterCoordinates index chessboard
          Chessboard.updateByCoordinates coordinates FieldSpace.removeCharacter chessboard
      
  
negative.code:     static member containsPickup (fieldSpace : FieldSpace) =
          fieldSpace.ContainsPickup
  
      // internal updaters
      
      static member updateCharacterOpt updater fieldSpace =
          { fieldSpace with CharacterOpt = updater fieldSpace.CharacterOpt }
  