yields falsehood1" will be grammatically correct, and Denoting0 phrase' denotes0 itself" – wrong. George Boolos, inspired by his student Michael Ernst, has written that the sentence might be syntactically ambiguous, in using multiple quotation marks whose exact mate marks cannot be determined. He revised traditional quotation into a system where the length of outer pairs of so-called q-marks of an expression is determined by the q-marks that appear inside the expression. This accounts not only for ordered quotes-within-quotes but also to, say, strings with an odd number of quotation marks. In Gödel, Escher, Bach: An Eternal Golden Braid, author Douglas Hofstadter suggests that the Quine sentence in fact uses an indirect type of self-reference. He then shows that indirect self-reference is crucial in many of the proofs of Gödel's incompleteness theorems. See also Grelling paradox List of paradoxes Quine, a computer program that produces its source code as output Self-reference Russell paradox Yablo's paradox References External links " "Logic and Language website Self-referential paradoxes Willard Van Orman Quine