In: Advanced Math
Suppose that D and E are sets, and D ⊆ E. Let A = P(E). Recall that P(E) denotes the set of all subsets of E. Define a relation R on A by
R = {(X, Y) ∈ A × A: [(X − Y) ∪ (Y − X)] ⊆ D}. So, XRY if and only if [(X−Y) ∪ (Y −X)] ⊆ D.
Prove that R is an equivalence relation on A.