In class, we proved that the set of regular languages is closed under union. The idea behind the proof was that, given two DFAs D1,D2, we could make a new DFA D3 which simultaneously keeps track of which state we're at in each DFA when processing a string.
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.
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.
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.
Regular languages are closed under complement, union, intersection, concatenation, Kleene star, reversal, homomorphism, and substitution.
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.
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.
Regular Languages are closed under complementation, i.e., if L is regular then L = Σ∗ \ L is also regular. Proof.
What are closure properties of regular languages? Regular languages are closed under complement, union, intersection, concatenation, Kleene star, reversal, homomorphism, and substitution.
The set of regular languages is closed under complementation. The complement of language L, written L, is all strings not in L but with the same alphabet. The statement says that if L is a regular lan- guage, then so is L. To see this fact, take deterministic FA for L and interchange the accept and reject states.