$tree->look_down(name => 'problem')->attr(value => $args{id});
my $contest = $tree->look_down(name => 'contest');
$contest->attr(value => $args{contest}) if $args{contest};
$contest->detach unless $args{contest}
} else {
$tree->look_down(name => 'problem')->attr(value => $args{id});
my $contest = $tree->look_down(name => 'contest');
$contest->attr(value => $args{contest}) if $args{contest};
$contest->detach unless $args{contest}
} else {