 The inverted Greek letter iota “\(\atoi\)” is used in PM, always followed by a variable, to begin a definite description. \((\atoi x) \phi x\) is read as “the \(x\) such that \(x\) is \(\phi\)”, or more simply, as “the \(\phi\)”. Such expressions may occur in subject position, as in \(\psi(\atoi x) \phi x\), read as “the \(\phi\) is \(\psi\)”. The formal part of Russell’s famous “theory of definite descriptions” consists of a definition of all formulas “…\(\psi(\atoi x) \phi x\)…” in which a description occurs. To distinguish the portion \(\psi\) from the rest of a larger sentence (indicated by the ellipses above) in which the expression \(\psi(\atoi x) \phi x\) occurs, the scope of the description is indicated by repeating the definite description within brackets: