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doc-src/TutorialI/Misc/prime_def.thy
author wenzelm
Tue, 18 Oct 2005 17:59:37 +0200
changeset 17904 21c6894b5998
parent 16417 9bc16273c2d4
permissions -rw-r--r--
simplified interfaces proof/proof' etc.: perform ProofHistory.apply(s)/current internally;
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(*<*)
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theory prime_def imports Main begin;
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paulson
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consts prime :: "nat \<Rightarrow> bool"
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(*>*)
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text{*
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\begin{warn}
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A common mistake when writing definitions is to introduce extra free
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variables on the right-hand side.  Consider the following, flawed definition
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(where @{text"dvd"} means ``divides''):
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@{term[display,quotes]"prime(p) == 1 < p & (m dvd p --> (m=1 | m=p))"}
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\par\noindent\hangindent=0pt
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Isabelle rejects this ``definition'' because of the extra @{term"m"} on the
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paulson
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right-hand side, which would introduce an inconsistency (why?).
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The correct version is
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@{term[display,quotes]"prime(p) == 1 < p & (!m. m dvd p --> (m=1 | m=p))"}
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\end{warn}
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*}
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(*<*)
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end
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(*>*)
isabelle