(Pardon the intrusion, but this exchange caught my eye for an unrelated reason. If you are feeling charitable, please indulge me for a moment as I ask about a side issue. If not, then just ignore it.)
I'm confused -- why wouldn't we say "Ta pani nie jest w domu?" "Tej pani nie ma w domu" is better? It doesn't make any sense. (Nor does "Tej pani nie ma w naszej grupie" for that matter.)
"Ta pani nie jest w domu." "This woman is not (at) home." -- makes sense. "Tej [why the change from "ta"] pani nie ma w domu." "This [?] woman does not have [in? at? on?] home." --- does not make sense ""Tej [?] pani nie ma w naszej grupie." "This woman does not have [in, at, on] our group." --- ???
This isn't a criticism, it is a question from someone who is struggling to learn the cases (and what they mean). What are these second and third sentences saying and why are they worded it in that way? Why is the first one wrong and the second one right? (I expected it to be the other way around: first is correct, second is ... strange. The third is also strange, and neither it nor the second one are comprehendible.)
(Again, apologies for the intrusion.)
Nie ma is about (unwanted) absence from something, whereas nie jest is about everything else.
To urządzenie nie jest w dobrym stanie = The device is not in a good condition (it's not literally absent from anything).
Tego urządzenia nie ma w sklepie. = There is no such device in the store (it's literally physically absent).
I believe that both nie ma w naszej grupie and nie jest w naszej grupie are acceptable, but I'd say that the latter is more likely, since "group" is a rather abstract term and less commonly refers to a gathering of people. But with "group" it's possible that the same situation may be interpreted both ways.
Okay, okay, hold your horses. Yes, this was something noticed after some time, that both versions should probably be accepted in most contexts. But so far seems like no one had time to do that in the whole course, which after all is constructed from thousands of sentences. I reported those that you commented on and now it's the contributors' decision to make. So yeah, I guess you are right, and it probably will gradually be changed, but maybe for the sake of your sanity you should consider focusing on 'this' instead of 'that'?
Polish does have a clear distinction between "ta" and "tamta", it's just that the distinction is different than between "this" and "that", so that can be translated to both "ta or "tamta", while "ta" can be "thia" or "that".
basically it's: this, that that ta, ta, tamta
if you are marked wrong in a sentence like this. please report next time. In most sentences both this and that should be accepted as translation of ta.