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    PR # 31237                                                                   
     The formation of multiple images of astronomical objects by gravitati       
     onal lensing was first discovered as the double QSO 0957+561. Up to n       
     ow more than 20 gravitational lensing candidate QSOs have been report       
     ed.  In more than half of these, the main lensing objects have been i       
     dentified. However, in some cases, the main lensing objects still hav       
     e not found although deep surveys in search of lensing objects have b       
     een performed. Here we propose asca observation of 3 dark gravitation       
     al lenses to identify dark lens objects by detecting X-ray emission f       
     rom the hot gas in the dark lens gravitational potential.  Even if no       
      X-ray emission is detected, our observations are very meaningful sin       
     ce we will confirm an existence of new type of objects which are dark       
     both in optical and in X-ray                                                
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