Assume A is an open set and B is a closed set. Determine if the following sets are definitely open, definitely closed, both, or neither.
3. Assume A is an open set and B is a closed set. Determine if the following sets are definitely open, definitely closed, both, or neither:
a. Closure of A U B
b. A - B
c. (Ac U B)c
d. (A ∩ B) U (A ∩ B)