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[roconnor AT theorem.ca]

On Wed, 9 Feb 2011, Satrajit Roy wrote:

> Also, I found an exercise in an older book (circa 1990s) which reads 
> something like: prove that
> (A=>B)=>(B=>A)

That was a typo.  It should read: prove that (A => B) => (not B => not A)

See <http://www.cs.kent.ac.uk/people/staff/sjt/TTFP/errata.html>

--
Russell O'Connor                                      <http://r6.ca/>
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''