Notice that regular languages are not closed under the subset/superset relation. For example, 01 is regular, but its subset {On1n : n >= 0} is not regular, but its subset {01, 0011, 000111} is regular again.
Regular languages are closed under complement, union, intersection, concatenation, Kleene star, reversal, homomorphism, and substitution.
The closure of regular languages under the regular operations of concatenation and union ensures that the result of applying these operations on regular languages always yields another regular language.
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.
A set is closed under an operation if applying that operation to any members of the set always yields a member of the set. For example, the positive integers are closed un- der addition and multiplication, but not divi- sion. Fact. The set of regular languages is closed under each Kleene operation.
Since every subset of a finite language is finite and every finite set is regular. Hence, every subset of a finite language is regular.
What are closure properties of regular languages? Regular languages are closed under complement, union, intersection, concatenation, Kleene star, reversal, homomorphism, and substitution.
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.
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.
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.