Closure Properties
Closure Properties. Lemma : Let A 1 and A 2 be two CF languages, then the union A 1 A 2 is context free as well. Proof : Assume that the two grammars are G 1 =(V 1 , ,R 1 ,S 1 ) and G 2 =(V 2 , ,R 2 ,S 2 ). Construct a third grammar G 3 =(V 3 , ,R 3 ,S 3 ) by:
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