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  TFenster = class (TObject)
  private
  ...
  public
  constructor Create(AParent: THaus);
  property Parent: THaus;
  end;

  THaus = class (TObject)
  private
    ...
  public
    constructor Create(AParent: TStrasse);
    ...
    property Fenster: TFenster;
    property Parent: TStrasse;
  end;					

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type
  THaus=class; // Vorwärtsdeklaration

  TFenster = class (TObject)  
    ...
  end;  

 
  THaus = class (TObject)  
   ...
  end;					

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type
  //forward declarations
  TFile = class;
  TFolderList = class;
  TFolder = class;

  TSoftwareRequirement = class(TFolder)
  private
  ...
  end;  
  TFolder = class(TFolderList)
    private
      fEnabled:boolean;
  ...
  end;
end;