for ( my $pos = 0 ; $pos < $#$puzzle_chars_ref ; $pos += 9 ) {

        # for better human readability
        if ( $pos > 0 and $pos % 27 == 0 ) { print $out "\n" }
        printf $out "%s%s%s %s%s%s %s%s%s\n",
          ( @$puzzle_chars_ref[ $pos .. $pos + 8 ] );
    }