 (The hat over a variable symbolizes the description operator: so “\(\hat{z}\)” means the \(z\) such that …) This is because (13) and (14) are logically equivalent, as are (15) and (16), while the only difference between (14) and (15) is that (14) contains the expression (Davidson calls it a “singular term”) “\(\hat{z} (z\! =\! z \amp R)\)” whereas (15) contains “\(\hat{z} (z\! =\! z \amp S)\)”,