standard / high
The Subset Cover Problem. The decision version of the subset cover problem asks if there are k or fewer subsets that cover all other subsets. A satisfying solution for k = 4 is the highlighted subsets.
Eblen et al. BMC Bioinformatics 2012 13(Suppl 10):S5 doi:10.1186/1471-2105-13-S10-S5