Let’s say I have a set $U$ containing some values. I randomly distribute these values into $n$ stacks and sort each stack from largest to smallest. Then I take the top $m$ items from each stack to form a set $S$.
What is the probability the largest $k$ values in $U$ are also in $S$? I can see trivially that the probability is $1$ if $m=k$ but that’s as far as I’ve got.