Boolean algebra differs from normal algebra in three different ways:
The values are of a logical and not of a numerical character.
The operations applicable to those values.
The properties of the operations. (Laws they obey).
If you have:
NOT ( A AND/OR B)
DeMorgan''s theorem equates it with:
( !A OR/AND !B)
In other words, negate both operands and switch an OR operator to AND (or switch an AND operator to OR).