 To distinguish terms that denote members of \(\bD\) from those that do not, free logic often employs the one-place “existence” predicate, ‘\(\rE!\)’ (sometimes written simply as ‘\(\rE\)’). For any singular term \(t\), \(\rE!t\) is true if \(t\) denotes a member of \(\bD\), false otherwise. ‘\(\rE!\)’ may be either taken as primitive or (in bivalent free logic with identity) defined as follows: