  With this notion of equinumerosity, Frege defined ‘the number of the concept \(F\)’ to be the extension consisting of all the concepts that are equinumerous with \(F\) (1884, §68). To get started, Frege then defined Zero to be the number of the concept being non-self-identical (1884, §74).  If we use the notation \(\#F\) to represent the number of the concept F, and use the \(\lambda\)-notation \([\lambda x \: \phi]\) to name the complex concept being an object x such that \(\phi\), Frege’s definition of Zero becomes: