ex 3.72 - merge consecutive equal values
ex 3.72 - group elements together
ex 3.72 - the correct stream
ex 3.72 - done
add functionality: {take,drop}-{while,until}
3.5.3 - estimate cos(x)
3.5.3 - time test
new util: `arith` for arithmetic comparisons
ex 2.1 - done
ex 2.2 - what?
ex 2.3 - 1
ex 2.3 - 2
ex 2.3 - done
ex 3.73 - done
ex 3.74 - done
ex 3.75 - done
ex 3.76 - done
ex 2.4 - done
ex 2.5 - done
ex 2.6 - auto test procedure