Let $A_1, ..., A_m$ be separable $n$-elements sets. We color elements of these sets in use of $2$ colors, but we consider two coloring as the same if one we can get from other by changing order of sets and then permuting elements inside sets. Find number of different coloring.
After some trying I failed during construction of polyi approach for this task (I had a problem with describing elements of group $S_n \oplus S_m$.
My another observation is trivial but maybe helpful there: Due to conditions, we can color each set $A_i$ on $n+1$ ways (we can choose if $0,1,...,n$ balls inside sets are white, other will be blue). That approach solves:
permuting elements inside sets.
But I have no idea how to consider this statement:
if one we can get from other by changing order of sets
Hint: consider $m \times n$ matrices with elements from $\{0,1\}$.