Exercise 2.37 (Minimized Disjunctive Normal Form). What can be said about the minimization of the following functions:

1 f1 = x1 ⊕ x2 ⊕ x3 ⊕ x4 ⊕ x5;

2 f2 = (x1 ∨ x2 ∨ x3)(x1 ∨ x2 ∨ x3) ⊕ x4 ⊕ x5;

3 f3 = (x1 ∨ x2 ∨ x3)(x1 ∨ x2 ∨ x3)(x4 ⊕ x5);

4 f4 = (x1 ⊕ x2 ⊕ x3)(x4 ⊕ x5 ⊕ x6);

5 f5 = (x1 ∨ x2 ∨ x3 ∨ x4 ∨ x5 ∨ x6)(x1 ∨ x2 ∨ x3 ∨ x4 ∨ x5 ∨ x6)?