 Paradoxes of self-reference have been known since antiquity. The discovery of the liar paradox is often credited to Eubulides the Megarian who lived in the 4th century BC. The liar paradox belongs to the category of semantic paradoxes, since it is based on the semantic notion of truth. Other well-known semantic paradoxes include Grelling’s paradox, Berry’s paradox, and Richard’s paradox.