Let $\mathcal L$ be a formal language.
An alphabet consists of the following parts:
Depending on the specific nature of any particular formal language, these too may be subcategorized.
Common examples of signs are parentheses, "(" and ")", and the comma, ",".
The logical connectives are also signs.
The symbols which comprise $\mathcal A$ are called the primitive symbols of $\mathcal A$.
Hence the distinction between these newly-introduced symbols and the primitive symbols.
Also denoted as
Some sources use $\Sigma$ to denote an arbitrary alphabet.
- 1988: Dominic Welsh: Codes and Cryptography ... (previous) ... (next): Notation: Alphabets and strings
- 1989: Ephraim J. Borowski and Jonathan M. Borwein: Dictionary of Mathematics ... (previous) ... (next): Entry: alphabet
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): Entry: alphabet