Theorem 1.1.3: For each regular language R ___* and each regular substitution s, s(R) is regular.
Corollary 1.1.4: For each regular language R ___* and each homomorphism h, h(R) is regular.
So far we know that the regular language family is closed under union, (set) concatenation, Kleene closure (star), regular substitution, and homomorphism.
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