The search box on Project Gutenberg uses a special syntax that actually allows more than just simple text searches. You can search by language, subject, author, and many others. For example:

• The search "l.german" will produce only texts in German.
• The search "s.shakespeare" will produce only texts about Shakespeare.
• The search "s.shakespeare l.german" will produce only texts in German about Shakespeare.

To see a more complete description of the syntax, go to the search page and click the "Help" button on the top-right of the page.

I haven't figured out how to search for terms with multiple words in these searches. Can someone figure it out? For example, how do you search for "william shakespeare" as a subject rather than just "shakespeare"? Or "old norse" as a language and not just "norse"?

Lath and plaster are both components of buildings.

(obsolete) Melancholy; a morbid depression.

Example: Tell your sister I dont want to hear any more about selling out and moving. That gives me the hypo whenever I think of it.

Source: Wiktionary

Via Wiktionary: A pile; a post or girder.

A pile in the above sense is "a large stake, or piece of pointed timber, steel etc., driven into the earth or sea-bed for the support of a building, a pier, or other superstructure, or to form a cofferdam, etc" (via Wiktionary).

Via Wiktionary: A massive structure, usually of stone, used as a pier, breakwater or junction between places separated by water.

A breakwater stops waves before they reach the port. Notice in the image below that the waves are violent on one side of the mole, but calm on the other.

He seems to be talking about Marcus Porcius Cato Uticensis, a Roman statesman who commited suicide with a sword.

What this page leaves implicit is that the chain rule is used to calculate the derivative of a composition of two functions. If the composition of f() and g() is f(g()), then the chain rule allows us to find the derivative of f(g()), or (in Leibniz notation):

df(g(x)) / dx.

This page is making the point that if we let u = g(x), then the derivative of the composition equals:

(df(u) / du) * (du / dx).

In the example at the bottom of the page, the reason we cannot simply use the power rule to find the derivative of (2x + 3)^5 is because the power rule is actually an application of the chain rule which only works when the base of the exponentiation is just x and the power is a constant real number. To see how to derive the power rule from other rules, see the Wikipedia page for Power rule. Then, try deriving (2x + 3)^5 by using the steps therein, and you will see that the answer is not (5)(2x + 3)^4.

DuckDuckGo has some optional special syntax if you need more control over your search. For example, intitle:, filetype:, and some logical expressions can be used. See here for a complete description of the syntax.

Additionally, the bang feature is useful, and you can browse all of the bangs here.