Empty string

The empty word is in theoretical and in practical computer science a word that consists of any single character, so the length of 0. It is also called the empty string. In many programming languages ​​, such a string is represented by a literal, in which the two start and stop characters, which include a string follow one another directly, such as " " in Perl or Java.

Definition

The empty word over the alphabet is a sequence of elements of length 0

Spelling

The empty word is usually represented by the Greek letter (epsilon English for " empty" ), often found but also the Greek letter (lambda, from the German " empty"). Other common representations are as different spelling of the epsilon, ( also for " empty" ) and as one element of a multiplicatively written monoid.

Features

Other features for special applications

Transitions in non-deterministic finite automata are tuples of the transition relation with states. Such a transition indicates that the state machine may change its state from to, without a sign is read. Transitions are thus one of the reasons for non-determinism. They are marked in the graph as edges are labeled with a.

Even with pushdown automata transitions are possible, meaning that by that state change the input word is not processed. If the topmost symbol substitutes for reading the contents of the basement in a transition through the empty word, it is so removed from the basement. Finally, the empty word symbolizes the empty stack, which is one of two possible acceptance criteria for pushdown automata.