Help with fixing unintended task duplication

[nucspl]

I'm trying to make a weekly reminder template, using dataview to take undone tasks from past reminders.

Here's the code:

task from "we are listing"
flatten file.lists as task
where task.fullyCompleted=false and contains(task.parent, null) = true

contains(task.parent, null) = true is meant to filter out subtasks, preventing its duplication as seen here:

Works great when there's only one root-level task.

But when there are multiple... oh boy.

I'm still pretty new to dataview so explanations and insights are greatly appreciated. Thanks in advance!

[nucspl]

I've resolved this the day after, turns out flatten was redundant.

task from #100/Reminders/Old
where fullyCompleted=false
group by file.link

[blacksmithgu]

Nice!