diff --git a/content/set-theory/spine/recursion.tex b/content/set-theory/spine/recursion.tex index c2e063b8..c65da945 100644 --- a/content/set-theory/spine/recursion.tex +++ b/content/set-theory/spine/recursion.tex @@ -58,20 +58,20 @@ For any term $\tau(x)$, we can explicitly define a term $\sigma(x)$, such that $\sigma(\alpha) = \tau(\funrestrictionto{\sigma}{\alpha})$ for any -ordinal $\alpha$. +ordinal~$\alpha$. \end{thm} \begin{proof} -For each $\alpha$, by \olref{transrecursionfun} there is a unique $\alpha$-approximation, $f_\alpha$, for $\tau$. Define $\sigma(\alpha)$ as $f_{\ordsucc{\alpha}}(\alpha)$. Now: +For each $\alpha$, by \olref{transrecursionfun} there is a unique $\alpha$-approximation, $f_\alpha$, for~$\tau$. Define $\sigma(\alpha)$ as $f_{\ordsucc{\alpha}}(\alpha)$. Now: \begin{align*} \sigma(\alpha) &= f_{\ordsucc{\alpha}}(\alpha) \\&= \tau(\funrestrictionto{f_{\ordsucc{\alpha}}}{\alpha}) \\&= \tau(\Setabs{\tuple{\beta, f_{\ordsucc{\alpha}}(\beta)}}{\beta \in \alpha}) \\&= - \tau(\Setabs{\tuple{\beta, f_{\alpha}(\beta)}}{\beta \in \alpha})\\&= + \tau(\Setabs{\tuple{\beta, f_{\ordsucc{\beta}}(\beta)}}{\beta \in \alpha})\\&= \tau(\funrestrictionto{\sigma}{\alpha}) \end{align*} -noting that $f_{\alpha}(\beta) = f_{\ordsucc{\alpha}}(\beta)$ for all $\beta < \alpha$, as in \olref{transrecursionfun}. +noting that $f_{\ordsucc{\beta}}(\beta) = f_{\ordsucc{\alpha}}(\beta)$ for all $\beta < \alpha$, as in \olref{transrecursionfun}. \end{proof} \noindent Note that \olref{transrecursionschema} is a \emph{schema}. Crucially, we cannot