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RATD.  Note 19

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TJ = Tom Johnston

TJ: My own thoughts about the difference between a row of
    a table (a tuple) and the table itself (a relation) is
    that the former is part of the extension of the relation,
    while the latter (more specifically, the set membership
    conditions which define it) represents the intension
    of the relation.

TJ: Next, that one cannot always infer the intensional rules