Part A: The difference A\B of two subsets A and B of is the set A∩( \B) of all points of which are in A but not in B. Show that if A, B ∈ F , then A \ B ∈ F .
Part B: The symmetric difference A △ B of two subsets A and B of is defined to be the set of points of which are in either A or B but not both. If A, B ∈ F , show that A △ B ∈ F .