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Time-travel is impossible and yet science fiction writers
from H.G.~Wells onwards have been fascinated by the idea the
fecundity of which has once again been shown by the recent
success of the \textit{Back to the Future} and the
\textit{Terminator} series of films.\footnote{For more
information about time-travel see Lem's `The Time-travel
Story' and Gardner's `Time Travel'.}

One narrative paradigm that has had several incarnations
involves the time-traveller being an art historian who is
interested in discovering more about a famous artist---in some
versions a painter and in others a sculptor---who \ldots
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