It's a perfectly sensible question. Knowing that both O(2^n) and O(3^n) are sets, and using the definition of set equality, it asks whether "f in O(2^n)" implie

It's a perfectly sensible question. Knowing that both O(2^n) and O(3^n) are sets, and using the definition of set equality, it asks whether "f in O(2^n)" implies "f in O(3^n)", and vice versa. Only one of the implications holds...