19. Completion. Let (2, B, P) be a probability space. Call a set N null if N e B and P(N) = 0. Call a set B C2 negligible if there exists a null set N such that BCN. Notice that for B to be...

Extracted text: 19. Completion. Let (2, B, P) be a probability space. Call a set N null if N e B and P(N) = 0. Call a set B C2 negligible if there exists a null set N such that BCN. Notice that for B to be negligible, it is not required that B be measurable. Denote the set of all negligible subsets by N. Call B complete (with respect to P) if every negligible set is null. What if B is not complete? Define B* := {AUM : A e B, M E N). (a) Show B* is a o-field.