iOS app: items in multiple lists?

Can anyone recommend an iOS task list or shopping list app that lets you
file items in multiple lists? So, for example, list A has items 1, 2 and 3;
and list B has items 3, 4 and 5; ticking off item 3 in list A also ticks it
off in list B.

Those few that I've found have been fiddly to say the least. I'd like it to
be quick and easy to add a task and select which lists it appears on.

Thanks.

-z-
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email: nettid1 at fastmail dot fm
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