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Closer property of Regular Language

 

1.  Regular Language closed under union.

 

If  L1 = Regular Language and L2 = Regular Language then L1 U L2 = Regular Language.

 

Example:

 

L1 = an , L2 = a2n  and L3 = a3n+5  then

L= L1 U  L2 U L3 = an  a2n  a3n + 5   it is also regular language

 

2.  Regular Language closed under intersection.

 

If L1= Regular Language and L2 = Regular Language then L1∩ L2 = Regular Language.

 

Example:

 

L1 = Mod 2  and L2 = Mod 4 then

L = L1 ∩ L2 = Mod 2 ∩ Mod 4 = Mod 4 = Regular Language

 

3.  Regular Language closed under concatenation.

 

If L1 = Regular Language and L2 = Regular Language then L1 . L2 = Regular Language.

 

Example:

 

L1 = an and L2 = a2n then L = L1. L2 = an . a2n = Regular Language

 

4. Regular Language closed under Complement.

 

If  L = Regular Language then LC = Regular Language

 

Example:

 

L = {At least three a i.e  |a| ≥ 3 }  then, 

LC = (a  3)C = {At most two a i.e. |a| < 3 or |a| ≤ 2}

{At most two a i.e. |a| < 3 or |a| ≤ 2} = Regular Language

 

5.  Regular Language closed under Kleene star operator.

 

If L = Regular Language then L*= Regular Language

 

Example:

 

L = an  then L* = (an)* = Regular Language

 

6. Regular Language closed under Set Difference.

 

If L1 = Regular Language and L2 = Regular Language then, 

L1 - L2 = L1  L2C = Regular Language.

 

Example:

 

L1 = Mod 2 = {2, 4, 6, 8, 10, 12, 14, 16, 20…} and L2 = Mod 4 = {4, 8, 12, 16, 20….}

Now L = L1 - L2 = {2, 6, 14, ….} = Regular Language

 

Regular Expression Closed Under:

 

Union (U), Intersection (), Concatenation (.), Complement, Kleene star operator (*), Set Difference, Symmetric Difference (⊕), NOR, XNOR, Reversal, Homomorphism, Inverse, Homomorphism.