 The piece of reasoning just carried out to prove the truth of \(KS\) should be available to any agent (person) with sufficient reasoning capabilities. That is, an agent should be able to prove the truth of \(KS\), and thus come to know that \(KS\) holds. However, if \(KS\) is known by someone, then what it expresses is not the case, and thus it cannot be true. This is a contradiction, and thus we have a paradox. The role of self-reference in this paradox is obvious, as it is based on a sentence, \(KS\), referring directly to itself.