openread  -- Operation, one input.  Abbreviation: openr
     The input to this procedure is a word, which must be a Unix  filename.
     It  can  contain slashes to indicate directory names.  If the file can
     be opened for reading,  the  output  from  the  procedure  is  a  file
     descriptor,  which  should  be stored in a variable for use in reading
     the file.  If the file cannot be opened, an error results.
