anchor.diff:      
       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.PassableCoordinates
       
       // used for both adding and relocating
       static member placeCharacter index coordinates (chessboard : Chessboard) =
  
positive.code:     member this.ContainsCharacter =
          match this.CharacterOpt with Some _ -> true | None -> false
  
      member this.ContainsPickup =
          match this.PickupItemOpt with Some _ -> true | None -> false
      
  
negative.code:         Map.add coordinates (updater passableCoordinates.[coordinates]) passableCoordinates
  
      static member updateByPredicateInternal predicate updater (passableCoordinates : Map<Vector2i, FieldSpace>) =
          Map.map (fun _ v -> if predicate v then updater v else v) passableCoordinates
      
      static member updateByCoordinates coordinates updater chessboard =
          Chessboard.updatePassableCoordinates (Chessboard.updateByCoordinatesInternal coordinates updater) chessboard
  