Prove the equations:

(a) \(\overline{\bar{A} \bar{B}}=A+B\);

(b) \(\overline{\bar{A}+\bar{B}}=A B\);

(c) \(\overline{A_{1}+A_{2}+\cdots+A_{n}}=\ddot{A}_{1} \bar{A}_{2} \ldots \bar{A}_{n}\)

(d) \(\overline{A_{1} A_{2} \ldots A_{n}}=\bar{A}_{1}+\overline{A_{2}}+\ldots+\bar{A}_{n}\)