0 votes 0 votes prince123 asked Dec 16, 2017 edited Dec 16, 2017 by prince123 prince123 246 views answer comment Share Follow See 1 comment See all 1 1 comment reply joshi_nitish commented Dec 16, 2017 reply Follow Share because of $\Gamma (Z,a)$. as only stack alphabet. you have one top of stack alphabet(Z) and one simple stack alphabet(a), now you can not use Z other than top of stack, and you are left with only 'a' for comparisons, here with 'a' as only comparing parameter-> "you can compare quantity but not quality" now, for anbn, you need to compare only quantity i.e no. of a's = no. of b's but for wwr or w#wr, you need to compare corresponding pairs in left half and right half i.e 'a' with 'a' and 'b' with 'b' which require comparison of both quantity and quality which cant be performed with above PDA, so answer is option 3 only 1 votes 1 votes Please log in or register to add a comment.