"Fermat's Last Theorem" and "Fermet's Enigma", by Simon Singh, are the same work.

Earlier notice and response:
'Fermat's Last Theorem' is the correct canonical title as listed on the official site of the author. 'Fermat's Enigma' is the altered title of the American edition.
response: I don't think you can call the title "canonical" if there the work is commonly available for sale under two different titles in English, and the history of changes to the field "Canonical title" supports this contention. For the purpose of disambiguation, perhaps we should just leave it at "Fermat's Last Theorem" and "Fermet's Enigma", by Simon Singh, are the same work.
response: In these cases the first edition in the country of the author's origin takes precedent.