EXIST

 EXIST = lv

 lv  Is a logical scalar memory reference that is
     assigned one of the following values:

 .TRUE.    If the specified file exists and can be opened 
           or if the unit exists
 .FALSE.   If the specified file or unit does not exist or 
           if the file exists but cannot be opened 

 The unit exists if it is a number in the range allowed by the
 processor.