doc-src/TutorialI/Misc/prime_def.thy
author wenzelm
Mon, 23 Jul 2007 19:45:47 +0200
changeset 23940 f2181804fced
parent 16417 9bc16273c2d4
permissions -rw-r--r--
marked some CRITICAL sections; eliminated transform_failure (to avoid critical section for main transactions); removed unused exceptions MetaSimplifier.SIMPROC_FAIL, Attrib.ATTRIB_FAIL, Method.METHOD_FAIL, Antiquote.ANTIQUOTE_FAIL;

(*<*)
theory prime_def imports Main begin;
consts prime :: "nat \<Rightarrow> bool"
(*>*)
text{*
\begin{warn}
A common mistake when writing definitions is to introduce extra free
variables on the right-hand side.  Consider the following, flawed definition
(where @{text"dvd"} means ``divides''):
@{term[display,quotes]"prime(p) == 1 < p & (m dvd p --> (m=1 | m=p))"}
\par\noindent\hangindent=0pt
Isabelle rejects this ``definition'' because of the extra @{term"m"} on the
right-hand side, which would introduce an inconsistency (why?). 
The correct version is
@{term[display,quotes]"prime(p) == 1 < p & (!m. m dvd p --> (m=1 | m=p))"}
\end{warn}
*}
(*<*)
end
(*>*)