diff -r d40cc6e7bfd8 -r aea72a834c85 doc-src/TutorialI/Recdef/document/termination.tex --- a/doc-src/TutorialI/Recdef/document/termination.tex Thu Nov 29 20:02:23 2001 +0100 +++ b/doc-src/TutorialI/Recdef/document/termination.tex Thu Nov 29 21:12:37 2001 +0100 @@ -24,12 +24,10 @@ \ \ {\isachardoublequote}f{\isacharparenleft}x{\isacharcomma}y{\isacharparenright}\ {\isacharequal}\ {\isacharparenleft}if\ x\ {\isasymle}\ y\ then\ x\ else\ f{\isacharparenleft}x{\isacharcomma}y{\isacharplus}{\isadigit{1}}{\isacharparenright}{\isacharparenright}{\isachardoublequote}\isamarkupfalse% % \begin{isamarkuptext}% -\noindent -Isabelle prints a -\REMARK{error or warning? change this part? rename g to f?} -message showing you what it was unable to prove. You will then -have to prove it as a separate lemma before you attempt the definition -of your function once more. In our case the required lemma is the obvious one:% +\noindent This definition fails, and Isabelle prints an error message +showing you what it was unable to prove. You will then have to prove it as a +separate lemma before you attempt the definition of your function once +more. In our case the required lemma is the obvious one:% \end{isamarkuptext}% \isamarkuptrue% \isacommand{lemma}\ termi{\isacharunderscore}lem{\isacharcolon}\ {\isachardoublequote}{\isasymnot}\ x\ {\isasymle}\ y\ {\isasymLongrightarrow}\ x\ {\isacharminus}\ Suc\ y\ {\isacharless}\ x\ {\isacharminus}\ y{\isachardoublequote}\isamarkupfalse% @@ -48,24 +46,24 @@ \noindent Because \isacommand{recdef}'s termination prover involves simplification, we include in our second attempt a hint: the \attrdx{recdef_simp} attribute -says to use \isa{termi{\isacharunderscore}lem} as -a simplification rule.% +says to use \isa{termi{\isacharunderscore}lem} as a simplification rule.% \end{isamarkuptext}% \isamarkuptrue% -\isacommand{consts}\ g\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequote}nat{\isasymtimes}nat\ {\isasymRightarrow}\ nat{\isachardoublequote}\isanewline +\isamarkupfalse% \isamarkupfalse% -\isacommand{recdef}\ g\ {\isachardoublequote}measure{\isacharparenleft}{\isasymlambda}{\isacharparenleft}x{\isacharcomma}y{\isacharparenright}{\isachardot}\ x{\isacharminus}y{\isacharparenright}{\isachardoublequote}\isanewline -\ \ {\isachardoublequote}g{\isacharparenleft}x{\isacharcomma}y{\isacharparenright}\ {\isacharequal}\ {\isacharparenleft}if\ x\ {\isasymle}\ y\ then\ x\ else\ g{\isacharparenleft}x{\isacharcomma}y{\isacharplus}{\isadigit{1}}{\isacharparenright}{\isacharparenright}{\isachardoublequote}\isanewline +\isacommand{recdef}\ f\ {\isachardoublequote}measure{\isacharparenleft}{\isasymlambda}{\isacharparenleft}x{\isacharcomma}y{\isacharparenright}{\isachardot}\ x{\isacharminus}y{\isacharparenright}{\isachardoublequote}\isanewline +\ \ {\isachardoublequote}f{\isacharparenleft}x{\isacharcomma}y{\isacharparenright}\ {\isacharequal}\ {\isacharparenleft}if\ x\ {\isasymle}\ y\ then\ x\ else\ f{\isacharparenleft}x{\isacharcomma}y{\isacharplus}{\isadigit{1}}{\isacharparenright}{\isacharparenright}{\isachardoublequote}\isanewline {\isacharparenleft}\isakeyword{hints}\ recdef{\isacharunderscore}simp{\isacharcolon}\ termi{\isacharunderscore}lem{\isacharparenright}\isamarkupfalse% +\isamarkupfalse% % \begin{isamarkuptext}% \noindent -This time everything works fine. Now \isa{g{\isachardot}simps} contains precisely -the stated recursion equation for \isa{g}, which has been stored as a +This time everything works fine. Now \isa{f{\isachardot}simps} contains precisely +the stated recursion equation for \isa{{\isacharquery}{\isacharquery}{\isachardot}f}, which has been stored as a simplification rule. Thus we can automatically prove results such as this one:% \end{isamarkuptext}% \isamarkuptrue% -\isacommand{theorem}\ {\isachardoublequote}g{\isacharparenleft}{\isadigit{1}}{\isacharcomma}{\isadigit{0}}{\isacharparenright}\ {\isacharequal}\ g{\isacharparenleft}{\isadigit{1}}{\isacharcomma}{\isadigit{1}}{\isacharparenright}{\isachardoublequote}\isanewline +\isacommand{theorem}\ {\isachardoublequote}f{\isacharparenleft}{\isadigit{1}}{\isacharcomma}{\isadigit{0}}{\isacharparenright}\ {\isacharequal}\ f{\isacharparenleft}{\isadigit{1}}{\isacharcomma}{\isadigit{1}}{\isacharparenright}{\isachardoublequote}\isanewline \isamarkupfalse% \isacommand{apply}{\isacharparenleft}simp{\isacharparenright}\isanewline \isamarkupfalse% @@ -78,22 +76,7 @@ If the termination proof requires a new lemma that is of general use, you can turn it permanently into a simplification rule, in which case the above \isacommand{hint} is not necessary. But our \isa{termi{\isacharunderscore}lem} is not -sufficiently general to warrant this distinction. - -The attentive reader may wonder why we chose to call our function \isa{g} -rather than \isa{f} the second time around. The reason is that, despite -the failed termination proof, the definition of \isa{f} did not -fail, and thus we could not define it a second time. However, all theorems -about \isa{f}, for example \isa{f{\isachardot}simps}, carry as a precondition -the unproved termination condition. Moreover, the theorems -\isa{f{\isachardot}simps} are not stored as simplification rules. -However, this mechanism -allows a delayed proof of termination: instead of proving -\isa{termi{\isacharunderscore}lem} up front, we could prove -it later on and then use it to remove the preconditions from the theorems -about \isa{f}. In most cases this is more cumbersome than proving things -up front. -\REMARK{FIXME, with one exception: nested recursion.}% +sufficiently general to warrant this distinction.% \end{isamarkuptext}% \isamarkuptrue% \isamarkupfalse%