Balance square brackets, fix duplicating section 4.2 bug

[brennennen]

On the beej.us site, there is a rendering bug around section 4.2 (it duplicates the entire section except the code snippet, see screen shot below). https://beej.us/guide/bgipc/html/split/pipes.html#the-search-for-pipe-as-we-know-it

See #12 for more details