Why it is called tetralogy?

"Tetralogy" refers to a work of literature consisting of four parts or volumes, typically related to each other in some way, such as sharing characters, themes, or a common setting.

The word "tetralogy" comes from the Greek words "tetra" meaning "four" and "logos" meaning "word" or "speech." So, literally, it means "four words" or "four speeches."

Here are some examples of tetralogies:

* The Lord of the Rings by J.R.R. Tolkien: This fantasy epic consists of four books: *The Fellowship of the Ring*, *The Two Towers*, *The Return of the King*, and *The Hobbit*.

* The Chronicles of Narnia by C.S. Lewis: This series of seven children's fantasy novels can be divided into four tetralogies.

* The Hitchhiker's Guide to the Galaxy by Douglas Adams: This science fiction series comprises six books, which are often considered as two trilogies. The first three books are a tetralogy.

* The Mill on the Floss by George Eliot: This novel is a four-part bildungsroman.

It's important to note that not all four-part works are considered tetralogies. The term is usually reserved for works where the four parts are intentionally connected in some way.