title: Pushdown Automata (PDA)
body: <p>I'm trying to write a pda pushdown automata that accept a^2n b^n, n>0
  but I'm not sure if the last part is correct</p>
  
  <pre><code>(p0, a, z0) = (p0, az0)
  (p0, a, a) = (p0, aa)
  (p0, b, a) = (p1, λ)
  (p1, λ, b) = (p2, λ)   &lt;=
  (p2, 0, b) = (p1, λ)  &lt;=
  (p2, λ, z0) = (p3, λ)  &lt;=
  </code></pre>