A list (finite set) of letters (cf. Letter). An alphabet usually contains the letters which are required to develop a certain system of symbols or, as is sometimes said, a language. For two alphabets and , their union , their intersection , their difference , as well as the inclusion relation are defined in the obvious manner. For convenience, the concept of an empty alphabet, i.e. an alphabet without any letters, may also be considered.
Alphabet. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Alphabet&oldid=14016