 A formal version of this argument, employing the term-forming, variable-binding class abstraction (or property abstraction) operator λ\(x\) (“the class of all \(x\) such that” or “the property of being such an \(x\) that”), was first formulated by Church (1943) in his review of Carnap’s Introduction to Semantics. Quine (1953), too, presents a variant of the slingshot using class abstraction, see also (Shramko and Wansing 2009a). Other remarkable variations of the argument are those by Kurt Gödel (1944) and Donald Davidson (1967, 1969), which make use of the formal apparatus of a theory of definite descriptions dealing with the description-forming, variable-binding iota-operator (ι\(x\), “the \(x\) such that”). It is worth noticing that the formal versions of the slingshot show how to move—using steps that ultimately preserve reference—from any true (false) sentence to any other such sentence. In view of this result, it is hard to avoid the conclusion that what the sentences refer to are just truth values.