diff -r f8353c722d4e -r a2bff98d6e5d doc-src/TutorialI/Misc/document/AdvancedInd.tex --- a/doc-src/TutorialI/Misc/document/AdvancedInd.tex Tue May 01 17:16:32 2001 +0200 +++ b/doc-src/TutorialI/Misc/document/AdvancedInd.tex Tue May 01 22:26:55 2001 +0200 @@ -79,7 +79,9 @@ you want to induct on a whole term, rather than an individual variable. In general, when inducting on some term $t$ you must rephrase the conclusion $C$ as -\[ \forall y@1 \dots y@n.~ x = t \longrightarrow C \] +\begin{equation}\label{eqn:ind-over-term} +\forall y@1 \dots y@n.~ x = t \longrightarrow C +\end{equation} where $y@1 \dots y@n$ are the free variables in $t$ and $x$ is new, and perform induction on $x$ afterwards. An example appears in \S\ref{sec:complete-ind} below. @@ -93,7 +95,20 @@ For an example see \S\ref{sec:CTL-revisited} below. Of course, all premises that share free variables with $t$ need to be pulled into -the conclusion as well, under the \isa{{\isasymforall}}, again using \isa{{\isasymlongrightarrow}} as shown above.% +the conclusion as well, under the \isa{{\isasymforall}}, again using \isa{{\isasymlongrightarrow}} as shown above. + +Readers who are puzzled by the form of statement +(\ref{eqn:ind-over-term}) above should remember that the +transformation is only performed to permit induction. Once induction +has been applied, the statement can be transformed back into something quite +intuitive. For example, applying wellfounded induction on $x$ (w.r.t.\ +$\prec$) to (\ref{eqn:ind-over-term}) and transforming the result a +little leads to the goal +\[ \bigwedge\vec{y}.~\forall \vec{z}.~ t(\vec{z}) \prec t(\vec{y}) \longrightarrow C(\vec{z}) + \Longrightarrow C(\vec{y}) \] +where the dependence of $t$ and $C$ on their free variables has been made explicit. +Unfortunately, this induction schema cannot be expressed as a single theorem because it depends +on the number of free variables in $t$ --- the notation $\vec{y}$ is merely an informal device.% \end{isamarkuptext}% % \isamarkupsubsection{Beyond Structural and Recursion Induction%