(5 points) A safe has five locks, v, w,x, y,z, all of which must be unlocked for the safe to open. The keys to the locks are distributed among five executives in the following manner: i. Mr. A has keys to v and x ii. Mr. B has keys to v and y iii. Mr. C has keys to w and y iv. Mr. D has keys to x and z v. Mr. E has keys to v and z o Determine the minimal number of executives required to open the case. o Find all combinations of executives that can open safe. Write an expression f(A, B,C, D,E) which specifies when the safe can opened. o Who is the essential executive without whom safe cannot be opened