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22 lines
623 B
22 lines
623 B
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Exercise 4.60: By giving the query
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(lives-near ?person (Hacker Alyssa P))
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Alyssa P. Hacker is able to find people who live near her, with whom she can
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ride to work. On the other hand, when she tries to find all pairs of people
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who live near each other by querying
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(lives-near ?person-1 ?person-2)
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she notices that each pair of people who live near each other is listed twice;
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for example,
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(lives-near (Hacker Alyssa P) (Fect Cy D))
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(lives-near (Fect Cy D) (Hacker Alyssa P))
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Why does this happen? Is there a way to find a list of people who live near
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each other, in which each pair appears only once? Explain.
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