Symmetric Difference is Associative/Proof 2

Theorem
Symmetric difference is associative:


 * $R * \left({S * T}\right) = \left({R * S}\right) * T$

Proof
Expanding the RHS:

Expanding the LHS:

From Intersection is Commutative, it can be seen that the LHS and RHS are the same, and the result is proved.