sub nextq {
      my $sz=8;
      (print("@_\n"),return) if @_ == $sz;
      o: foreach my $col(0..$sz-1) {
          my($u,$d)=(scalar(@_),scalar(@_));
          for (@_) {next o if($_==$col or $_==$col-$u-- or $_==$col+$d--)}
          nextq(@_,$col);
      }
  }
  nextq();