Indicate that Kleene's theorem involves induction

sketches.tex

@@ -36,7 +36,7 @@
     && \bot &\sqsubseteq x\\
     \implies && \phi(\bot) &\sqsubseteq \phi(x) = x \tag{\(\phi\) is \defn{monotone}{mono.}}\\
     \implies && \phi^2(\bot) &\sqsubseteq \phi^2(x) = \phi(x) = x\\
-    &&&\;\;\vdots\\
+    &&&\;\;\vdots \; \tag{i.e.\ induction}\\
     % \implies && \phi^n(\bot) &\sqsubseteq \phi^n(x) = \dots = x\\
     % &&&\;\;\vdots\\
     \implies && \underline{\mu\phi} = \bigsqcup_{i = 0}^\infty \phi^i(\bot) &\sqsubseteq \bigsqcup_{i = 0}^\infty \phi^i(x) = \underline{x}