22.1 problem 1
 22.2 problem 2
 22.3 problem 3
 22.4 problem 4
 22.5 problem 5
 22.6 problem 6
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 22.10 problem 10
 22.11 problem 11
 22.12 problem 12
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 22.14 problem 14
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 22.17 problem 17
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 22.20 problem 20
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 22.24 problem 24
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 22.27 problem 27
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 22.70 problem 70
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 22.75 problem 75
 22.76 problem 76