The SOR$BEGIN_SORT routine initializes a sort operation by
    opening input and output files and by passing the key information
    and any sort options.

    Format

      SOR$BEGIN_SORT  [key_buffer] [,lrl] [,options] [,file_alloc]

                      [,user_compare] [,user_equal] [,sort_process]

                      [,work_files] [,context]