Let L be a. context-free language over and a e 2. Define era(L) to be the set obtained by removing all occurrences of a from strings of L. era(L) is the language L with a erased. For example, if abab, bach, aa E L, then bb, bcb, and e E er (L). Prove that era(L) is context-free. Hint: Convert the grammar that generates L to one that generates era(L) b, and e E era (L). Prove that era(L)