Push down automata
Exercise 1. Write PDAs for the following languages:
1.1. $ L = \{\: w \in \{A,B\}^* \ | \:w \text{ is a palindrome}\} $
1.2. $ L = \{\: w \in \{A,B\}^* \ | \: \text{#}A(w) \neq \: \text{#}B(w) \} $
1.3. $ L = \{ A^{m} B^{m+n} C^{n} \ | \: n, m \geq 0 \} $
1.4. $ L = \{ A^{n}B^{n}C^{m}D^{m} | \: \ n,m \geq 0 \} \cup \{ A^nB^mC^mD^n | \: \ n,m \geq 0 \} $
1.5. $ L = \{ A^{i}B^{j}C^{k} | \: \text{ i=j or j=k} \} $
Exercise 2. Acceptance by empty stack.
Consider the following definition for an accepted word, by a PDA: $(q_{0}, w, Z_{0}) \vdash (q,e,e)$ where $ q $ is any state from K.
Prove that a language is CF if it can be accepted by a PDA via the empty-stack definition.
(Hint, you need to prove two parts)