Editing Diagonal lemma (section)

=== Gödel Numbering ===
The diagonal lemma also requires a [[Gödel numbering]] <math>\alpha</math>. We write <math>\alpha (\varphi)</math> for the code assigned to <math>\varphi</math> by the numbering. For <math>\overline{n}</math>, the standard numeral of <math>n</math> (i.e. <math>\overline{0} =_{df} \mathsf{0}

</math> and <math>\overline{n+1} =_{df} \mathsf{S}(\overline{n}) </math>), let  <math>\ulcorner \varphi \urcorner </math> be the standard numeral of the code of <math>\varphi</math> (i.e. <math>\ulcorner \varphi \urcorner </math> is <math>\overline{\alpha(\varphi)}</math>). We assume a [[Gödel's encoding|standard Gödel numbering]]