The principle of duality states that the dual of a logical expression is obtained by replacing AND (.) with OR (+) and vice versa, and replacing 1s with 0s and 0s with 1s. For example, the dual of the expression A+B=0 is A.B=1, where + is replaced with . and 0 is replaced with 1.

2. According to principle of duality
"Dual of one expression is
obtained by replacing AND (.)with
OR(+) and OR with AND together
with replacement of 1 with 0 and
0 with 1.

3. For example: consider the expression
A+B=0. The dual of this expression is
obtained by replacing + with . and 0
by 1.
i.e., A.B=1 is dual of A+B=0