 Let us stipulate that where \(\Pi\) is any 1-place concept term (name or variable), the notation ‘\(\epsilon\Pi\)’ designates the extension of the concept \(\Pi\). So, for example, \(\epsilon F\) denotes the extension of the concept \(F\). Note that 1-place \(\lambda\)-expressions of the form \([\lambda x\,\phi]\) are 1-place concept terms, and so \(\epsilon[\lambda x\,\phi]\) is well-formed and designates the extension of the concept \([\lambda x\,\phi]\). Thus, whereas Frege used \(\stackrel{,}{\epsilon}\) as a variable-binding operator that binds an object variable in a formula to produce the name of an extension, we are using \(\epsilon\) as a term-forming function symbol that applies to 1-place concept terms to produce terms denoting, or ranging over, objects. Thus, when \(\epsilon\) is prefixed to a concept name, the resulting expression is a name of an object, and in particular, a name of the extension of the concept denoted by the concept name. When the \(\epsilon\) is prefixed to a concept variable, e.g., as in \(\epsilon F\), the resulting expression is a kind of complex variable that ranges over extensions: for each value of the variable \(F\), \(\epsilon F\) denotes the extension of \(F\).