doc-src/TutorialI/Misc/document/let_rewr.tex
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     1 \begin{isabelle}%
       
     2 \isacommand{lemma}~{"}(let~xs~=~[]~in~xs@ys@xs)~=~ys{"}\isanewline
       
     3 \isacommand{apply}(simp~add:~Let\_def)\isacommand{.}%
       
     4 \begin{isamarkuptext}%
       
     5 If, in a particular context, there is no danger of a combinatorial explosion
       
     6 of nested \texttt{let}s one could even add \texttt{Let_def} permanently:%
       
     7 \end{isamarkuptext}%
       
     8 \isacommand{theorems}~[simp]~=~Let\_def\end{isabelle}%