| author | Walther Neuper <neuper@ist.tugraz.at> |
| Thu, 12 Aug 2010 15:03:34 +0200 | |
| branch | isac-from-Isabelle2009-2 |
| changeset 37913 | 20e3616b2d9c |
| parent 16417 | 9bc16273c2d4 |
| permissions | -rw-r--r-- |
| nipkow@8745 | 1 |
(*<*) |
| haftmann@16417 | 2 |
theory prime_def imports Main begin; |
| paulson@11457 | 3 |
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 |
| paulson@11456 | 8 |
variables on the right-hand side. Consider the following, flawed definition |
| paulson@11456 | 9 |
(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 |
| nipkow@9792 | 12 |
Isabelle rejects this ``definition'' because of the extra @{term"m"} on the
|
| paulson@11456 | 13 |
right-hand side, which would introduce an inconsistency (why?). |
| paulson@11456 | 14 |
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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(*>*) |