What's more, we've seen that regular languages are closed under union, concatenation and Kleene star. This means every regular expression defines a regular language.
The closure property states that if L1 and L2 are regular languages, then their union L1 ∪ L2 is also a regular language. This means that any string belonging to either L1 or L2, or both, can be recognized by a finite automaton or expressed using a regular expression.
Regular languages are closed under union, intersection, complement etc. I understand the definition of closure, which means that when we apply some operation on some element of the set, the resulting element should also be in the set.
Closure properties on regular languages are defined as certain operations on regular language that are guaranteed to produce regular language. Closure refers to some operation on a language, resulting in a new language that is of the same “type” as originally operated on i.e., regular.
Intersection. Theorem If L1 and L2 are regular languages, then the new language L = L1 ∩ L2 is regular. Proof By De Morgan's law, L = L1 ∩ L2 = L1 ∪ L2. By the previous two theorems this language is regular.
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.
No. The intersection of an infinite set of regular languages is not necessarily even computable. The closure of regular languages under infinite intersection is, in fact, all languages. The language of “all strings except s” is trivially regular.
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.
Languages in P are also closed under reversal, intersection, union, concatenation, Kleene closure, inverse homomorphism, and complementation.