Final answer:
The expression equivalent to !(weekday || holiday) is !weekday && !holiday, following De Morgan's laws that translate the negation of a disjunction into a conjunction of negations.
Step-by-step explanation:
The expression that is equivalent to !(weekday || holiday) is !weekday && !holiday. The original expression uses the NOT operator (!) on the result of an OR (||) operation. By applying De Morgan's laws, which state that !(A || B) is equivalent to !A && !B, we can transform the original expression into one that uses AND (&&) and NOT (!) operators on the individual variables without changing the logical meaning of the expression.
The correct answer is option a) !weekday && !holiday. This is because the NOT operator negates the whole condition of it being either a weekday or a holiday, meaning it's neither a weekday nor a holiday.