of symbols may be considered as well (see Omega language).

Strings are often written as the concatenation of their symbols, and when using this notational convention it is convenient for practical purposes to restrict the symbols in an alphabet so that this notation is unambiguous. For instance, if the two-member alphabet is {00,0}, a string written in concatenated form as "000" is ambiguous because it is unclear if it is a sequence of three "0" symbols, a