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Concrete mathematics : a foundation for computer science

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4 EXERCISES 151<br />

64 The Peirce sequence 3’~ of order N is an infinite string of fractions<br />

separated by ‘ 0 and n 6 N (including fractions that are not reduced).<br />

It is defined recursively by starting with<br />

For N > 1, we <strong>for</strong>m ?$,+I by inserting two symbols just be<strong>for</strong>e the kNth<br />

symbol of ?N, <strong>for</strong> all k > 0. The two inserted symbols are<br />

k-l<br />

- ZI<br />

N+l ’<br />

k-l<br />

yN,kN - N+l’<br />

if kN is odd;<br />

if kN is even.<br />

Here ?N,j denotes the jth symbol of Y’ N, which will be either ‘

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