Use the algorithm. When you have created the grammar, then for the word aba, which is in L, write the sequence of instantaneous descriptions as the (possibly modified) npda accepts this word and write the corresponding derivation in the grammar you constructed. Hint: note conditions 1 and 2 on page 209, 7th edition

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16. Find a context-free grammar that generates the language accepted by the npda M=({q0,q1},{a,b},{A, z},,q0,z,{q1}), with transitions (q0,a,z)(q0,b,A)(q0,a,A)={(q0,Az)}={(q0,AA)}={(q1,)}