Feedback from 2-26

- [ ] Example of the effect of mutating state on an outer closure
```ex
  outer = -1
  IO.puts "BEGIN: outer=#{outer}"
  [1, 2, 3]
  |> Enum.each fn i ->
    IO.puts "BEFORE: i=#{i}, outer=#{outer}"
    outer = i
    IO.puts "AFTER:  i=#{i}, outer=#{outer}"
  end
  IO.puts "END: outer=#{outer}"

``` 