设任意x∈(A∩B)-(A∩C) <=>(x∈A∧x∈B)∧x∉A∩C <=> (x∈A∧x∈B)∧(x∉A∨x∉C) <=> (x∈A∧x∈B∧x∉A)∨(x∈A∧x∈B∧x∉C) <=>F∨(x∈A∧x∈B∧x∉C) <=>x∈A∧x∈B∧x∉C <=>x∈A∧x∈B-C <=> x∈A∩(B-C)
