 where \(A\)! stands for a primitive theoretical predicate ‘being abstract’, \(xF\) is to be read as “\(x\) encodes \(F\)” and [λy q] is a propositional property (“being such a \(y\) that \(q\)”). That is, according to this definition, “the extension of \(p\) is the abstract object that encodes all and only the properties of the form [λy q] which are constructed out of propositions \(q\) materially equivalent to \(p\)” (Anderson and Zalta 2004: 14).