ex 1.15 - done
ex 1.16 - done
ex 1.17 - done
ex 1.18 - done
ex 1.19 - done
ex 1.20 - done
ex 1.21 - done
ex 1.22 - done
ex 1.23 - done
ex 3.65 - done
3.5.3 - inf stream of pairs - working
3.5.3 - infinite streams of pairs
ex 3.66 - the formula
ex 3.66 - the answer
ex 3.66 - done
ex 3.67 - done
ex 3.68 - done
ex 3.69 - triple impl
ex 3.69 - done
ex 3.70 - merge impl