Solution
= Solution
The commutativity and associativity of <set intersection> give
$$
\begin{aligned}
(A\setminus B)\setminus C
&=A\cap B^c\cap C^c\\
&=A\cap C^c\cap B^c\\
&=\boxed{(A\setminus C)\setminus B}.
\end{aligned}
$$
Equivalently, part (ii) reduces both sides to removal of the same <set union> $B\cup C=C\cup B$.