0 votes 0 votes X belongs to {a,b}* such that n(a)<n(b)<2n(a) is a CFL. Please somebody explain the push and pop sequences of the alphabets on the stack. I'm not being able to visualise, how it is CFL? Theory of Computation context-free-language theory-of-computation + – aambazinga asked Sep 18, 2018 aambazinga 276 views answer comment Share Follow See 1 comment See all 1 1 comment reply smsubham commented Sep 18, 2018 reply Follow Share The first thing you should keep in mind that its non deterministic CFL and not deterministic CFL (former is more powerful) How push pop is performed? push all a's. Then we have to pop one a after seeing n(a) to 2* n(a) (exact number is depends on string, this is the why there is non determinism). For example, w= abb push a then pop one a for two b. w= aabbb. pop one a for first two b then one a for last b. If w = aab It wouldn't be accepted as for first b we can pop one a but then we are left with no b but stack isn't empty. 0 votes 0 votes Please log in or register to add a comment.