Which of the following is true?a)All subsets of a regular set are alwa...
Explanation:
Regular set is defined as a set of strings that can be generated by a regular grammar or recognized by a finite automaton. Now, let's analyze each option to find the true statement.
Option A: All subsets of a regular set are always regular.
This statement is not true. A counterexample can be a regular set A = {a, ab}, whose subsets are A1 = {ε}, A2 = {a}, A3 = {ab}, A4 = {a, ab}. Here, A3 and A4 are not regular sets.
Option B: All finite subsets of non-regular set are always regular.
This statement is true. A non-regular language is one that cannot be generated by a regular grammar or recognized by a finite automaton. Therefore, any finite subset of a non-regular set can only contain finite strings that can be generated or recognized by a finite automaton, and hence, it is always regular.
Option C: Union of two non-regular sets of language is not regular.
This statement is not true. A counterexample can be two non-regular sets A = {a^n b^n | n ≥ 0} and B = {a^n b^n c^n | n ≥ 0}. Both these sets are not regular, but their union A ∪ B = {a^n b^n | n ≥ 0} ∪ {a^n b^n c^n | n ≥ 0} = {a^n b^n c^m | n, m ≥ 0} is a regular set.
Option D: Infinite times union of finite sets is always regular.
This statement is not true. A counterexample can be an infinite set A = {a^n | n ≥ 0}, whose finite subsets are all regular sets. But, the infinite union of all these finite subsets gives the set A itself, which is not regular. Therefore, the infinite times union of finite sets is not always regular.
Hence, the correct option is B.
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