Formal definition If A is a regular language, A (Kleene star) is a regular language. Due to this, the empty string language {ε} is also regular. If A and B are regular languages, then A ∪ B (union) and A • B (concatenation) are regular languages. No other languages over Σ are regular.
A regular language is one which has an FA or an RE. Regular languages are closed under union, concatenation, star, and complementation.
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.
Regular Languages are closed under complementation, i.e., if L is regular then L = Σ∗ \ L is also regular. Proof.
Let L be a regular language, and M be an NFA that accepts it. Here, δR is δ with the direction of all the arcs reversed. Thus, it is proved that L is closed under reversal.
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.
Closure property holds for addition and multiplication of whole numbers. Closure property of whole numbers under addition: The sum of any two whole numbers will always be a whole number, i.e. if a and b are any two whole numbers, a + b will be a whole number. Example: 12 + 0 = 12. 9 + 7 = 16.
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.
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.
Regular Languages are closed under intersection, i.e., if L1 and L2 are regular then L1 ∩ L2 is also regular. L1 and L2 are regular • L1 ∪ L2 is regular • Hence, L1 ∩ L2 = L1 ∪ L2 is regular.