Closure Properties of Regular Languages Given a set, a closure property of the set is an operation that when applied to members of the set always returns as its answer a member of that set. For example, the set of integers is closed under addition.
Closure under Union For any regular languages L and M, then L ∪ M is regular. Proof: Since L and M are regular, they have regular expressions, say: Let L = L(E) and M = L(F). Then L ∪ M = L(E + F) by the definition of the + operator.
Regular languages are closed under concatenation - this is demonstrable by having the accepting state(s) of one language with an epsilon transition to the start state of the next language. If we consider the language L = {a^n | n >=0}, this language is regular (it is simply a).
Regular languages are closed under complement, union, intersection, concatenation, Kleene star, reversal, homomorphism, and substitution.
CFL's are closed under union, concatenation, and Kleene closure. Also, under reversal, homomorphisms and inverse homomorphisms. But not under intersection or difference. Let L and M be CFL's with grammars G and H, respectively.
Closure property states that any operation conducted on elements within a set gives a result which is within the same set of elements. Integers are either positive, negative or zero. They are whole and not fractional. Integers are closed under addition.
Decision Properties: Approximately all the properties are decidable in case of finite automaton. (i) Emptiness. (ii) Non-emptiness. (iii) Finiteness. (iv) Infiniteness. (v) Membership. (vi) Equality.
A closure property of a language class says that given languages in the class, an operator (e.g., union) produces another language in the same class. Example: the regular languages are obviously closed under union, concatenation, and (Kleene) closure.
In programming languages, a closure, also lexical closure or function closure, is a technique for implementing lexically scoped name binding in a language with first-class functions. Operationally, a closure is a record storing a function together with an environment.