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References
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There is a paper by Aho, Beeri and Ullman
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Aho Beeri Ullman Theory Joins Relational
.]
and one with Beeri replaced by Sagiv.
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Aho Sagiv Ullman Equivalence Relational Expressions
.]
Chandra and Merlin also contributed to the field.
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Chandra Merlin Queries Relational
.]
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References
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