Here you could also say "Az alma nincs a szék alatt".
Not to forget that van is needed to indicate the proposition.
It's really confusing as to when "van" is needed and when not.
Why not 'az alma a szék nem alatt van': the apple is somewhere though not under the chair?
I don't believe that you can negate a postposition. If that were legitimate, then it would imply that the apple had some other spatial relationship with the chair, such as being on it. The apple is somewhere about the chair, but not under it.
Köszönöm szépen. I think the moral is then not to insert anything between a noun and its postposition, even to negate it.
Yes, I think that that would be a wise move.
Could 'all' instead of 'van' be accepted? (It's not been accepted in my case)