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    PR # 31254                                                                   
     We propose to observe the highest z clusters of galaxies to obtain X-       
     ray luminosity function. The redshifts of currently proposed targets        
     range from 0.56-0.82 and for these highest z samples. ROSAT showed th       
     e feasibility of detection and suggest further evidence of negative e       
     volution of XLF. This type of observation is essentially important fo       
     r understanding the evolution of the X-ray properties of clusters and       
      is one of the foremost modern cosmology.                                   
                                                                                 
                                                                                 
                                                                                 
                                                                                 
                                                                                 
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