> For the complete documentation index, see [llms.txt](https://mandober.gitbook.io/math-debrief/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mandober.gitbook.io/math-debrief/600-toc/620-formal-language-theory/alphabet.md).

# Alphabet

<https://en.wikipedia.org/wiki/Alphabet_(formal_languages>)

* formal language
* formal language theory
* string (word)
* symbol (letter)
* alphabet

In formal language theory, a **string** is a finite sequence of symbols, formed by concatenating the elements of an underlying base set; this base set is called the *alphabet of a string*.

The members of the alphabet are called **symbols**, and the written symbols of a natural language are better known as letters, although sometimes the symbols may also be referred to as characters, digits or glyphs.

The **binary alphabet**, `Σ = {0,1}`, has only two symbols as members, but still, an infinite number of **binary strings** may be formed from it.

<https://en.wikipedia.org/wiki/Alphabet_(formal_languages>) <https://en.wikipedia.org/wiki/Array_data_structure> <https://en.wikipedia.org/wiki/Combinatorics_on_words> <https://en.wikipedia.org/wiki/Formal_language> <https://en.wikipedia.org/wiki/Sequence> <https://en.wikipedia.org/wiki/String_(computer_science>) <https://en.wikipedia.org/wiki/String-searching_algorithm> <https://en.wikipedia.org/wiki/Symbol_(programming>) <https://en.wikipedia.org/wiki/Variable-width_encoding>