((A-B)-C)∪((A-B)∩C)∪((A∩B)-C)∪(A∩B∩C) = ((A∩~B)∩~C)∪((A∩~B)∩C)∪((A∩B)∩~C)∪(A∩B∩C) = (A∩(~B∩~C))∪(A∩(~B∩C))∪(A∩(B∩~C))∪(A∩B∩C) = A∩((~B∩~C)∪(~B∩C)∪(B∩~C)∪(B∩C)) = A∩((~B∩(~C∪C))∪(B∩(~C∪C))) = A∩(~B∪B) = A