Let \((X, \mathcal {M}, \mu )\) be a measure space and \(f : X \to Y\) be a function.
- Show that \(\mathcal {N} = \{f^{-1}A : A \in \mathcal {M}\}\) is a \(\sigma \)-algebra.
- Let \(\nu (B) = \mu (f(B))\) for \(B \in \mathcal {N}\). Show that \(\nu \) is a measure.
- Show that even if \((X, \mathcal {M}, \mu )\) is complete we do not necessarily have that \((Y, \mathcal {N}, \nu )\) is complete.