[amp_mcq option1=”At least one” option2=”At most one” option3=”nan” option4=”All” correct=”option1″]
The correct answer is: A. At least one.
A Horn clause is a clause with at least one positive literal. A literal is an atomic formula or its negation. A clause is a disjunction of literals. A positive literal is an atomic formula that is not negated. A negative literal is the negation of an atomic formula.
For example, the following are Horn clauses:
- $p \lor q$
- $\neg p \lor r$
- $\neg p \lor \neg q \lor r$
The following are not Horn clauses:
- $p \land q$
- $p \lor \neg q$
- $\neg p \land r$
In the first example, there are two positive literals, $p$ and $q$. In the second example, there is one positive literal, $\neg p$. In the third example, there are no positive literals.
Horn clauses are important in logic programming, where they are used to represent facts and rules. They are also used in artificial intelligence, where they are used to represent knowledge and to solve problems.